Variable color digital measuring instrument for sequentially exhibiting measured values

ABSTRACT

A variable color digital measuring instrument sequentially exhibits measured values in a color in accordance with the relation of the present measured value to a past measured value. A memory, controlled by a timer, is provided for storing data representing the past measured value. A comparator compares the present measured value with the data stored in the memory and develops a comparison signal accordingly, which is then used to control the color of the presently exhibited measured value.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a division of my copending application Ser. No. 08/910,080, filed on Aug. 12, 1997, entitled Variable Color Display System, which is a division of my application Ser. No. 08/571,246, filed on Dec. 12, 1995, entitled Variable Color Display System, now U.S. Pat. No. 5,656,935 issued on Aug. 12, 1997, which is a division of my application Ser. No. 08/187,350, filed on Jan. 27, 1994, entitled Variable Color Digital Multimeter, now U.S. Pat. No. 5,475,300 issued on Dec. 12, 1995, which is a division of my application Ser. No. 07/865,460, filed on Apr. 9, 1992, entitled Variable Color Digital Multimeter, now U.S. Pat. No. 5,283,517 issued on Feb. 1, 1994, which is a division of my application Ser. No. 07/628,328, filed on Dec. 14, 1990, entitled Variable Color Digital Multimeter, now U.S. Pat. No. 5,122,733 issued on Jun. 16, 1992, which is a division of my application Ser. No. 07/197,322, filed on May 23, 1988, entitled Variable Color Digital Multimeter, now abandoned, which is a division of my application Ser. No. 06/819,111, filed on Jan. 15, 1986, entitled Variable Color Digital Multimeter, now U.S. Pat. No. 4,794,383 issued on Dec. 27, 1988.

Reference is also made to my related applications Ser. No. 06/817,114, filed on Jan. 8, 1986, entitled Variable Color Digital Timepiece, now U.S. Pat. No. 4,647,217 issued on Mar. 3, 1987, Ser. No. 06/919,425, filed on Oct. 16, 1986, entitled Electronic Timepiece with transducers, now U.S. Pat. No. 4,687,340 issued on Aug. 18, 1987, Ser. No. 06/926,511, filed on Nov. 3, 1986, entitled Electronic Timepiece with Physical Transducer, now U.S. Pat. No. 4,705,406 issued on Nov. 10, 1987, Ser. No. 07/150,913, filed on Feb. 1, 1988, entitled Variable Color Display Typewriter, now U.S. Pat. No. 4,824,269 issued on Apr. 25, 1989, Ser. No. 07/336,080, filed on Apr. 11, 1989, entitled Variable Color Display Typewriter, now U.S. Pat. No. 4,934,852 issued on Jun. 19, 1990, Ser. No. 06/839,526, filed on Mar. 14, 1986, entitled Variable Color Display Telephone, now U.S. Pat. No. 4,726,059 issued on Feb. 16, 1988, Ser. No. 06/940/100, filed on Dec. 10, 1986, entitled Digital Voltmeter with Variable Color Background, now U.S. Pat. No. 4,831,326 issued on May 16, 1989, Ser. No. 06/922,847, filed on Oct. 24, 1986, entitled Continuously Variable Color Display Device, now U.S. Pat. No. 4,845,481 issued on Jul. 4, 1989, Ser. No. 07/322,341, filed on Mar. 13, 1989, entitled Continuously Variable Color Optical Device, now U.S. Pat. No. 4,965,561 issued on Oct. 23, 1990, Ser. No. 07/379,616, filed on Jul. 14, 1989, entitled Variable Color Digital Display for Emphasizing Position of Decimal Point, now U.S. Pat. No. 5,003,298 issued on Mar. 26, 1991, Ser. No. 06/920,740, filed on Oct. 20, 1986, entitled Step Variable Color Display Device, now abandoned, Ser. No. 06/931,626, filed on Nov. 17, 1986, entitled Variable Color Hybrid Display Device, now abandoned, Ser. No. 07/157,603, filed on Feb. 19, 1988, entitled Variable Color Multiplexed Display System, now abandoned, and Ser. No. 07/000,478, filed on Jan. 5, 1987, entitled Variable Color Digital Tachometer, now abandoned, which describe the devices employing a variable color display.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to measuring instruments utilizing a variable color digital display.

2. Description of the Prior Art

A display device described in U.S. Pat. No. 3,740,570, issued on Jun. 19, 1973 to George R. Kaelin et al., uses special LEDs that exhibit different colors when subjected to different currents. The LEDs are biased by pulses of different amplitudes, to achieve different colors of the display, and by the length inversely proportional to the pulse amplitude, to compensate for variable brightness of the display caused by different amplitudes of the pulses.

A circuit employing a dual-color LED driven by a dual timer is described in the article by Bill Wagner entitled 2-color LED+driver=versatile visual effects, published on Oct. 2, 1980 in EDN volume 25, No. 19, page 164. Since dual-color LEDs are connected to conduct currents in opposite directions, it would be impossible to forwardly bias them simultaneously.

An electronic display having segments wherein each segment is capable of selectively illuminating two colors is disclosed in U.S. Pat. No. 4,488,149 issued on Dec. 11, 1984 to William A. Givens, Jr. Two AND gates are provided for biasing, in each display segment, either a first light emitting diode, for emitting a first color, or a second light emitting diode, for emitting a second color. It is not contemplated to illuminate both light emitting diodes in each segment simultaneously for blending the colors.

A multi-colour LED display for seven segment figures is disclosed in German Patent No. 3,009,416 issued on Sep. 17, 1981 to Klaus Gillessen. The LED circuit consists of seven group of diodes, each group made up of two diodes, one red and one green. The cathodes of all red diodes are terminated in a common connection, and the green ones likewise, the anodes of each pair of diodes being common for that pair. Two transistors connected in cascade are utilized for activating either all green LEDs, or all red LEDs, but not both simultaneously. When a low level signal is applied to the base of the first transistor, the first transistor is blocked, and the second transistor is turned ON to illuminate the second set of the diodes. When a high level signal is applied to the input of the first transistor, the first transistor is turned ON, while the second transistor is blocked, whereby the first set of the diodes is illuminated. Since the first transistor cannot be simultaneously turned ON and OFF, it would be impossible to illuminate the two sets of the diodes simultaneously. In another embodiment is shown a multi-colour LED display utilizing three sets of LEDs: red, green, and blue, which are respectively commonly connected and may be activated by manual switches. It is not contemplated that the three sets of LEDs be activated in selective combinations to blend the colors.

A digital electrooptical display with anti-parallel light emitting diodes is disclosed in East German Patent No. 220,844 issued on Apr. 10, 1985 to Thomas Hoffmann et al.

Two light emitting diodes for emitting light of different colors are connected in each segment back-to-back. Since the light emitting diodes are connected to conduct currents in opposite directions, it would be impossible to illuminate them simultaneously, because the opposite currents attempting to pass through a single conductor would cancel. A system for measuring radioactivity is described in U.S. Pat. No. 2,643,344, issued on Jun. 23, 1953 to Ian H. McLaren et al. Another systems for measuring radioactivity are described in U.S. Pat. No. 2,648,015 issued on Aug. 4, 1953 to Alexander Greenfield et al., and in U.S. Pat. No. 2,682,000 issued on Jun. 22, 1954 to Joseph F. Clayton et al. Since these three patents are very similar, they are equally authoritative. The system for measuring radioactivity, disclosed in the three patents, includes an analog pointer indicator having three scales, with three associated colored light bulbs, for indicating which scale is applicable for the reading of the measured value. A mechanism for automatic range selection is provided, which is controlled by two solenoids, and which also controls the three associated colored light bulbs. In response to the range selection, one of the light bulbs illuminates the indicator face with a distinctive color to indicate which measurement scale is applicable.

A digital meter is disclosed in U.S. Pat. No. 2,889,518, issued on Jun. 2, 1959 to Harold R. Hudson et al. The digital meter includes a motor, a wheel counter rotatable by the motor, a potentiometer rotatable by the motor, and a mechanical sampler (vibrator). An unknown voltage is compared, by the sampler, with an instant reference voltage that appears on the wiper of the potentiometer. The motor keeps rotating the potentiometer until the unknown voltage is equal to the reference voltage. The rotation of the motor is then automatically stopped, which also stops the wheel counter, whose position numerically indicates the value of the measured voltage. The decimal point monochromatic lamps are placed between the wheels of the counter. One of the decimal point lamps is illuminated, by manually operated range switch, to indicate by its position the selected measurement range. A continuous graphical display of barometric data is disclosed in U.S. Pat. No. 5,178,010, issued on Jan. 12, 1993 to Thomas M. Holzel. An electronic trace of barometric pressure is presented across a display on which the trace, grid and axis labels are scrolled horizontally. The display is updated from stored data on a continuous basis so that an entire week of uninterrupted barometric data can be presented.

A solid-state barometer is described in application note SSAN-9 published in the 1983 SenSym Pressure Transducer Handbook, page 9-30.

The prior art measuring instruments do not contemplate that a digital indication of the presently measured value may be colored in accordance with its relation to a past measured value.

SUMMARY OF THE INVENTION

In a broad sense, it is the principal object of this invention to provide an improved variable color digital measuring instrument.

It is another object of the invention to provide a variable color digital measuring instrument for sequentially exhibiting the measured values.

It is still another object of the invention to provide a variable color digital measuring instrument with a memory for storing from time to time the measured values.

It is still another object of the invention to provide a variable color digital measuring instrument with a comparator for comparing the measured values with the values stored in the memory.

It is still another object of the invention to provide a variable color digital measuring instrument for controlling the color of the exhibited measured values in accordance with their relation to the values stored in a memory.

It is still another object of the invention to provide a variable color digital measuring instrument for controlling the color of the exhibited measured values in accordance with their relation to the previous measured values.

In summary, a variable color digital measuring instrument of the invention includes a plurality of adjacent variable color light emitting diode digital display elements for sequentially providing a digital indication of a first measured value of a signal and of a second measured value of a signal, in a timing relationship determined by a timer.

The invention resides in the provision of a memory, for storing the prior measured value of the signal, of a comparator, for performing a comparison of the present measured value of the signal with the value stored in the memory, and of a color control, for controlling the color of the digital indication in accordance with the result of the comparison.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings in which are shown several possible embodiments of the invention,

FIG. 1 is a block diagram of a typical prior art monochromatic digital display system.

FIG. 2 is a generalized block diagram of a variable color digital display system for the practice of the present invention.

FIG. 3 is a block diagram of a step variable color display system.

FIG. 4 is a block diagram of a continuously variable color display system.

FIG. 5 is a block diagram of 2-primary color digital display.

FIG. 6 is a block diagram of 3-primary color digital display.

FIG. 7 is an enlarged detail of one digit of 2-primary color digital display.

FIG. 8 is an enlarged cross-sectional view of one display segment in FIG. 7, taken along the line 8--8.

FIG. 9 is an enlarged detail of one digit of 3-primary color digital display.

FIG. 10 is an enlarged cross-sectional view of one display segment in FIG. 9, taken along the line 10--10.

FIG. 11 is a schematic diagram of one digit of 2-primary color control circuit of this invention.

FIG. 12 is a schematic diagram of one digit of 3-primary color control circuit of this invention.

FIG. 13 is a block diagram of a color control logic circuit for controlling 2-primary color display.

FIG. 14 is a block diagram of a color control logic circuit for controlling 3-primary color display.

FIG. 15 is a schematic diagram of a color control logic circuit for controlling 2-primary color display.

FIG. 16 is a schematic diagram of a color control logic circuit for controlling 3-primary color display.

FIG. 17 is a simplified schematic diagram, similar to FIG. 11, showing how the number `7` can be displayed in three different colors.

FIG. 18 is a simplified schematic diagram, similar to FIG. 12, showing how the number `1` can be displayed in seven different colors.

FIG. 19 is a block diagram of 2-primary color 4-digit display.

FIG. 20 is a block diagram of 3-primary color 4-digit display.

FIG. 21 is a block diagram of a signal converter for 2-primary color display.

FIG. 22 is a block diagram of a signal converter for 3-primary color display.

FIG. 23 is a schematic diagram of a comparator circuit for 2-primary color display.

FIG. 24 is a graph showing the relationship between the inputs and outputs of the comparator circuit in FIG. 23.

FIG. 25 is a schematic diagram of a comparator circuit for 3-primary color display.

FIG. 26 is a graph showing the relationship between the inputs and outputs of the comparator circuit in FIG. 25.

FIG. 27 is a block diagram of a continuously variable color display system utilizing two primary colors.

FIG. 28 is a block diagram of a continuously variable color display system utilizing three primary colors.

FIG. 29 is an expanded block diagram of FIG. 27.

FIG. 30 is an expanded block diagram of FIG. 28.

FIG. 31 is a schematic diagram of a scaling circuit.

FIG. 32 is a schematic diagram of an A/D converter and memory combination of FIGS. 29 and 30.

FIG. 33 is a schematic diagram of a memory and color converter combination of FIG. 29.

FIG. 34 is a timing diagram of the circuit shown in FIG. 33.

FIG. 35 is a schematic diagram of a memory and color converter combination of FIG. 30.

FIG. 36 is a timing diagram of the circuit shown in FIG. 35.

FIG. 37 is a continuation of the timing diagram of FIG. 36.

FIG. 38 is a graphic representation of TABLE 1.

FIG. 39 is a graphic representation of TABLE 2.

FIG. 40 is a graph of the ICI chromaticity diagram.

FIG. 41 is a block diagram of a multimeter with variable color digital display.

FIG. 42 is a block diagram of a multimeter with multiplexed variable color digital display.

FIG. 43 is a block diagram of a digital multimeter with a display that can change color in accordance with external control.

FIG. 44 is a block diagram of a digital multimeter with a display that can change color in accordance with internal control.

FIG. 45 is a block diagram of a digital multimeter with a display that can change color in accordance with measurement quantity.

FIG. 46 is a block diagram of a digital multimeter with a display that can change color in accordance with measurement location.

FIG. 47 is a simplified schematic diagram of a variable color digital multimeter for measuring outputs of different transducers.

FIG. 48 is a simplified schematic diagram of a variable color digital multimeter for measuring signals from different locations.

FIG. 49 is a simplified schematic diagram of a variable color digital multimeter for measuring signals by different methods.

FIG. 50 is a simplified schematic diagram of a variable color digital thermometer.

FIG. 51 is a simplified schematic diagram of a digital ampermeter with variable color range indication.

FIG. 52 is a simplified schematic diagram of a digital voltmeter with variable color range indication.

FIG. 53 is a simplified schematic diagram of a digital ohmmeter with variable color range indication.

FIG. 54 is a detail of the multimeter shown in FIGS. 51, 52, and 53.

FIG. 55 is a simplified schematic diagram of a digital voltmeter for displaying positive and negative measurement results in respectively different colors.

FIG. 56 is a simplified schematic diagram of a variable color display system for displaying decimal numbers such that digits preceding and following the decimal point are displayed in respectively different colors.

FIG. 57 is a timing diagram of the circuit shown in FIG. 56.

FIG. 58 is a simplified schematic diagram of a variable color display system for displaying integers and decimal numbers in respectively different colors.

FIG. 59 is a block diagram of a variable color display device for selectively displaying output digital data from different digital devices in respectively different colors.

FIG. 60 is a simplified schematic diagram of a variable color digital barometer.

FIG. 61 is a simplified schematic diagram of a digital multimeter for displaying measurement results in accordance with time.

FIG. 62 is a block diagram of a variable color digital multimeter with comparator and memory.

FIG. 63 is a block diagram of a variable color digital multimeter with comparator and memory for high and low limits.

FIG. 64 is a block diagram of a variable color digital multimeter with comparator and memory for previous measurement values.

FIG. 65 is a block diagram of a variable color digital multimeter with memory for previous measurement errors.

FIG. 66 is a schematic diagram of a comparator with low and high measurement limits.

FIG. 67 is a schematic diagram of a comparator and error counter.

FIG. 68 is a detail of the comparator, error flip-flop, and color control combination.

FIG. 69 is a detail of the comparator, error memory, and color converter combination.

FIG. 70 is a detail of the low measurement limit memory and comparator combination.

FIG. 71 is a detail of the error counter and PROM combination.

FIG. 72 is a schematic diagram of a variable color digital multimeter with registered comparator for comparing instant measured values with previously stored ones.

FIG. 73 is a block diagram of a variable color digital multimeter with uniform color control for all display digits.

FIG. 74 is a block diagram of a variable color digital multimeter with independent color control for each display digit.

FIG. 75 is a block diagram of a dual digital voltmeter with single variable color digital display.

FIG. 76 is a block diagram of a variable color RMS digital voltmeter with variable color crest factor indication.

FIG. 77 is the RMS and crest factor chart.

FIG. 78 is an expanded block diagram of a crest factor converter with ratio producing circuit.

FIG. 79 is an expanded block diagram of a crest factor converter with precision divider.

FIG. 80 is a schematic diagram of an RMS-to-DC converter.

FIG. 81 is a schematic diagram of a peak detector.

FIG. 82 is an expanded block diagram of 2-primary color control for the crest factor converter.

FIG. 83 is an expanded block diagram of 3-primary color control for the crest factor converter.

FIG. 84 is an expanded block diagram of 2-primary color converter for the crest factor converter.

FIG. 85 is an expanded block diagram of 3-primary color converter for the crest factor converter.

FIG. 86 is a front view of a variable color digital multimeter of the present invention.

FIG. 87 is a block diagram of a variable color digital multimeter controlled by a microprocessor.

FIG. 88 is an expanded block diagram of a variable color digital multimeter for indicating front and rear measurements in different colors.

FIG. 89 is an expanded block diagram of a variable color digital multimeter for indicating DC, AC, and OHMS measurements in respectively different colors.

FIG. 90 is an expanded block diagram of a variable color digital multimeter for indicating measurements with filter and without filter in different colors.

Throughout the drawings, like characters indicate like parts.

BRIEF DESCRIPTION OF THE TABLES

In the tables which show examples of the relationship between an input voltage, memory contents, and resulting color in the color converter of the present invention,

TABLE 1 shows the characteristic of a step variable 2-primary color converter.

TABLE 2 shows a rainbow-like characteristic of a continuously variable 3-primary color converter.

Throughout the tables, memory addresses and data are expressed in a well known hexadecimal notation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now, more particularly, to the drawings, in FIG. 1 is shown a block diagram of a typical prior art digital display system which usually includes a device 10a for developing digital data, a suitable decoder 20 for converting the digital data into a displayable code, and a monochromatic digital display 30 for indicating the digital data visually.

As shown in FIG. 2, the present invention resides in the substitution of a commercially well known monochromatic digital display with a variable color digital display 40, and in the addition of a color control circuit 50 for controlling the color of display 40. The variable color digital display system of this invention can simultaneously indicate the values of two different quantities, from the outputs of respective devices 10b, 10c, by causing the value of the first quantity to be indicated on display 40 in digital format, and by controlling the color of display 40 in accordance with the value of the second quantity.

In FIG. 3 is shown a block diagram of another embodiment of a variable color digital display system of the present invention, characterized by a step variable color control circuit 51.

In FIG. 4 is shown a block diagram of still another embodiment of variable color digital display system, characterized by a continuously variable color control circuit 56.

In FIG. 5 is shown a block diagram of a 2-primary color display system including a commercially well known 7-segment display decoder driver 22, a variable color 7-segment display element 42, and a 2-primary color control logic circuit 52. The decoder driver 22 accepts a 4-bit BCD (binary coded decimal) code at its inputs A0, A1, A2, A3 and develops output drive signals at its outputs a, b, c, d, e, f, g, and DP (decimal point) to drive respective segments of 7-segment display element 42. The color control circuit 52 accepts color control logic signals at its inputs R (red), Y (yellow), and G (green) and develops at its outputs drive signals for red bus 5 and green bus 6, respectively, to illuminate display element 42 in a selected color.

In FIG. 6 is shown a block diagram of a 3-primary color display system including a 7-segment display decoder driver 22, variable color 7-segment display element 43, and a 3-primary color control logic circuit 53. The color control circuit 53 accepts color control logic signals at its inputs R (red), Y (yellow), G (green), BG (blue-green), B (blue), P (purple), and W (white) and develops at its outputs drive signals for red bus 5, green bus 6, and blue bus 7, respectively, to illuminate display element 43 in a selected color.

In FIG. 7, the 2-primary color display element includes seven elongated display segments a, b, c, d, e, f, and g, arranged in a conventional pattern, which may be selectively energized in different combinations to display the desired digits. Each display segment includes a pair of LEDs (light emitting diodes): red LED 2 and green LED 3, which are closely adjacent such that the light signals emitted therefrom are substantially superimposed upon each other to mix the colors. To facilitate the illustration, the LEDs are designated by segment symbols, e. g., the red LED in the segment a is designated as 2a, etc.

In FIG. 8, red LED 2e and green LED 3e are placed on the base of a segment body 15a which is filled with a transparent light scattering material 16. When forwardly biased, LEDs 2e and 3e emit light signals of red and green colors, respectively, which are scattered within transparent material 16, thereby blending the red and green light signals into a composite light signal that emerges at the upper surface of segment body 15a. The color of the composite light signal may be controlled by varying the portions of the red and green light signals.

In FIG. 9, each display segment of the 3-primary color display element includes a triad of LEDs: red LED 2, green LED 3, and blue LED 4, which are closely adjacent such that the light signals emitted therefrom are substantially superimposed upon one another to mix the colors.

In FIG. 10, red LED 2e, green LED 3e, and blue LED 4e are placed on the base of a segment body 15b which is filled with a transparent light scattering material 16. Red LEDs are typically manufactured by diffusing a p-n junction into a GaAsP epitaxial layer on a GaAs substrate; green LEDs typically use a GaP epitaxial layer on a GaP substrate; blue LEDs are typically made from SiC material.

When forwardly biased, LEDs 2e, 3e, and 4e emit light signals of red, green, and blue colors, respectively, which are scattered within transparent material 16, thereby blending the red, green, and blue light signals into a composite light signal that emerges at the upper surface of segment body 15b. The color of the composite light signal may be controlled by varying the portions of the red, green, and blue light signals.

In FIG. 11 is shown a schematic diagram of a 2-primary color common cathodes 7-segment display element 42 which can selectively display various digital fonts in different colors on display segments a, b, c, d, e, f, g, and DP (Decimal Point). The anodes of all red and green LED pairs are interconnected in each display segment and are electrically connected to respective outputs of a commercially well known common-cathode 7-segment decoder driver 23. The cathodes of all red LEDs 2a, 2b, 2c, 2d, 2e, 2f, 2g, and 2i are interconnected to a common electric path referred to as a red bus 5. The cathodes of all green LEDs 3a, 3b, 3c, 3d, 3e, 3f, 3g, and 3i are interconnected to a like common electric path referred to as a green bus 6.

The red bus 5 is connected to the output of a tri-state inverting buffer 63a, capable of sinking sufficient current to forwardly bias all red LEDs 2a to 2i in display element 42. The green bus 6 is connected to the output of a like buffer 63b. The two buffers 63a, 63b can be simultaneously enabled by applying a low logic level signal to the input of inverter 64a, and disabled by applying a high logic level signal thereto. When buffers 63a, 63b are enabled, the conditions of red bus 5 and green bus 6 can be selectively controlled by applying suitable logic control signals to the bus control inputs RB (red bus) and GB (green bus), to illuminate display element 42 in a selected color. When the buffers 63a, 63b are disabled, both red bus 5 and green bus 6 are effectively disconnected to cause display element 42 to be completely extinguished.

In FIG. 12 is shown a schematic diagram of a 3-primary color common anodes 7-segment display element 43 which can selectively display digital fonts in different colors. The cathodes of all red, green, and blue LED triads in each display segment are interconnected and electrically connected to respective outputs of a commercially well known common anode 7-segment decoder driver 24. The anodes of all red LEDs 2a, 2b, 2c, 2d, 2e, 2f, and 2g are interconnected to form a common electric path referred to as a red bus 5. The anodes of all green LEDs 3a, 3b, 3c, 3d, 3e, 3f, and 3g are interconnected to form a like common electric path referred to as a green bus 6. The anodes of all blue LEDs 4a, 4b, 4c, 4d, 4e, 4f, and 4g are interconnected to form a like common electric path referred to as a blue bus 7.

The red bus 5 is connected to the output of a non-inverting tri-state buffer 62a, capable of sourcing sufficient current to illuminate all red LEDs 2a to 2g in display element 43. The green bus 6 is connected to the output of a like buffer 62b. The blue bus 7 is connected to the output of a like buffer 62c. The three buffers 62a, 62b, and 62c can be simultaneously enabled, by applying a low logic level signal to the input of inverter 64b, and disabled by applying a high logic level signal thereto. When buffers 62a, 62b, and 62c are enabled, the conditions of red bus 5, green bus 6, and blue bus 7 can be selectively controlled by applying valid combinations of logic level signals to the bus control inputs RB (red bus), GB (green bus), and BB (blue bus), to illuminate display element 43 in a selected color. When buffers 62a, 62b, and 62c are disabled, red bus 5, green bus 6, and blue bus 7 are effectively disconnected to cause display element 43 to be completely extinguished.

STEP VARIABLE COLOR CONTROL

In FIG. 13 is shown a logic circuit 69a for developing drive signals for red bus 5 and green bus 6, to control the color of display element 42 shown in FIG. 11. Two voltage levels, referred to as logic high and low, are used throughout the description of the digital circuits. The color of display element 42 may be controlled by applying valid combinations of logic level signals to its color control inputs R (red), Y (yellow), and G (green). The logic circuit 69a combines the input signals in a logic fashion and develops output drive signals RB (red bus) and GB (green bus), for activating red bus 5 and green bus 6, respectively, of display element 42.

In FIG. 14 is shown a like logic circuit 69b for developing drive signals for red bus 5, green bus 6, and blue bus 7, to control the color of display element 43 shown in FIG. 12. The color of display element 43 may be controlled by applying valid combinations of logic level signals to its color control inputs B (blue), P (purple), BG (blue-green), G (green), Y (yellow), W (white), and R (red). The logic circuit 69b combines the input signals in a logic fashion and develops output drive signals RB (red bus), GB (green bus), and BB (blue bus), for activating red bus 5, green bus 6, and blue bus 7, respectively, of display element 43.

Exemplary schematic diagrams of the color control logic circuits shown in FIGS. 15 and 16 consider active high logic levels, which means that only the selected color control input is maintained at a high logic level, while all remaining color control inputs are maintained at a low logic level. The circuit in FIG. 15 is a detail of the color control logic circuit 69a employing 2-input logic OR gates 60a and 60b, interposed between the color control inputs R, Y, G and bus control outputs RB, GB, in a manner which will become more apparent from the description below. A like circuit in FIG. 16 is a detail of the color control logic circuit 69b employing 4-input logic OR gates 61a, 61b, and 61c similarly interposed between the color control inputs B, P, BG, G, Y, W, R and bus control outputs RB, GB, BB. It will be obvious to those skilled in the art that other types of logic devices may be effectively used.

The operation of display element 42 shown in FIG. 11 will be now explained by the example of illuminating a digit `7` in three different colors. A simplified schematic diagram to facilitate the explanation is shown in FIG. 17. Any digit between 0 and 9 can be selectively displayed by applying the appropriate BCD code to the inputs A0, A1, A2, and A3 of common-cathode 7-segment decoder driver 23. The decoder driver 23 develops at its outputs a, b, c, d, e, f, g, and DP drive signals for energizing selected groups of the segments to thereby visually display the selected number, in a manner well known to those having ordinary skill in the art. To display decimal number `7`, a BCD code 0111 is applied to the inputs A0, A1, A2, and A3. The decoder driver 23 develops high voltage levels at its outputs a, b, and c, to illuminate equally designated segments a, b, and c, and low voltage levels at all remaining outputs (not shown), to extinguish all remaining segments d, e, f, and g.

To illuminate display element 42 in red color, the color control input R is raised to a high logic level, and the color control inputs Y and G are maintained at a low logic level. As a result, the output of OR gate 60a rises to a high logic level, thereby causing the output of buffer 63a to drop to a low logic level. The current flows from the output a of decoder driver 23, via red LED 2a and red bus 5, to current sinking output of buffer 63a. Similarly, the current flows from the output b of decoder driver 23, via red LED 2b and red bus 5, to the output of buffer 63a. The current flows from the output c of decoder driver 23, via red LED 2c and red bus 5, to the output of buffer 63a. As a result, segments a, b, and c illuminate in red color, thereby causing a visual impression of a character `7`. The green LEDs 3a, 3b, 3c remain extinguished because the output of buffer 63b is at a high logic level, thereby disabling green bus 6.

To illuminate display element 42 in green color, the color control input G is raised to a high logic level, while the color control inputs R and Y are maintained at a low logic level. As a result, the output of OR gate 60b rises to a high logic level, thereby causing the output of buffer 63b to drop to a low logic level. The current flows from the output a of decoder driver 23, via green LED 3a and green bus 6, to current sinking output of buffer 63b. Similarly, the current flows from the output b of decoder driver 23, via green LED 3b and green bus 6, to the output of buffer 63b. The current flows from the output c of decoder driver 23, via green LED 3c and green bus 6, to the output of buffer 63b. As a result, segments a, b, and c illuminate in green color. The red LEDs 2a, 2b, and 2c remain extinguished because the output of buffer 63a is at a high logic level, thereby disabling red bus 5.

To illuminate display element 42 in yellow color, the color control input Y is raised to a high logic level, while the color inputs R and G are maintained at a low logic level. As a result, the outputs of both OR gates 60a and 60b rise to a high logic level, thereby causing the outputs of both buffers 63a and 63b to drop to a low logic level. The current flows from the output a of decoder driver 23, via red LED 2a and red bus 5, to current sinking output of buffer 63a, and, via green LED 3a and green bus 6, to current sinking output of buffer 63b. Similarly, the current flows from the output b of decoder driver 23, via red LED 2b and red bus 5, to the output of buffer 63a, and, via green LED 3b and green bus 6, to the output of buffer 63b. The current flows from the output c of decoder driver 23, via red LED 2c and red bus 5, to the output of buffer 63a, and, via green LED 3c and green bus 6, to the output of buffer 63b. As a result of blending light of red and green colors in each segment, segments a, b, and c illuminate in substantially yellow color.

The operation of display element 43 shown in FIG. 12 will be now explained by the example of illuminating a digit `1` in seven different colors. A simplified schematic diagram to facilitate the explanation is shown in FIG. 18. To display decimal number `1`, a BCD code 0001 is applied to the inputs A0, A1, A2, and A3 of common anode 7-segment decoder driver 24. The decoder driver 24 develops low voltage levels at its outputs b and c, to illuminate equally designated segments b and c, and high voltage levels at all remaining outputs (not shown), to extinguish all remaining segments a, d, e, f, and g.

To illuminate display element 43 in red color, the color control input R is raised to a high logic level, while all remaining color control inputs are maintained at a low logic level. As a result, the output of OR gate 61a rises to a high logic level, thereby causing the output of buffer 62a to rise to a high logic level. The current flows from the output of buffer 62a, via red bus 5 and red LED 2b, to the output b of decoder driver 24, and, via red LED 2c, to the output c of decoder driver 24. As a result, segments b and c illuminate in red color, thereby causing a visual impression of a character `1`. The green LEDs 3b, 3c and blue LEDs 4b, 4c remain extinguished because green bus 6 and blue bus 7 are disabled.

To illuminate display element 43 in green color, the color control input G is raised to a high logic level, while all remaining color control inputs are maintained at a low logic level. As a result, the output of OR gate 61b rises to a high logic level, thereby causing the output of buffer 62b to rise to a high logic level. The current flows from the output of buffer 62b, via green bus 6 and green LED 3b, to the output b of decoder driver 24, and, via green LED 3c, to the output c of decoder driver 24. As a result, segments b and c illuminate in green color.

To illuminate display element 43 in blue color, the color control input B is raised to a high logic level, while all remaining color control inputs are maintained at a low logic level. As a result, the output of OR gate 61c rises to a high logic level, thereby causing the output of buffer 62c to rise to a high logic level. The current flows from the output of buffer 62c, via blue bus 7 and blue LED 4b, to the output b of decoder driver 24, and, via blue LED 4c, to the output c of decoder driver 24. As a result, segments b and c illuminate in blue color.

To illuminate display element 43 in yellow color, the color control input Y is raised to a high logic level, while all remaining color control inputs are maintained at a low logic level. As a result, the outputs of OR gates 61a and 61b rise to a high logic level, thereby causing the outputs of buffers 62a and 62b to rise to a high logic level. The current flows from the output of buffer 62a, via red bus 5 and red LED 2b, to the output b of decoder driver 24, and, via red LED 2c, to the output c of decoder driver 24. The current also flows from the output of buffer 62b, via green bus 6 and green LED 3b, to the output b of decoder driver 24, and, via green LED 3c, to the output c of decoder driver 24. As a result of blending light of red and green colors in each segment, the segments b and c illuminate in substantially yellow color.

To illuminate display element 43 in purple color, the color control input P is raised to a high logic level, while all remaining color control inputs are maintained at a low logic level. As a result, the outputs of OR gates 61a and 61c rise to a high logic level, thereby causing the outputs of buffers 62a and 62c to rise to a high logic level. The current flows from the output of buffer 62a, via red bus 5 and red LED 2b, to the output b of decoder driver 24, and, via red LED 2c, to the output c of decoder driver 24. The current also flows from the output of buffer 62c, via blue bus 7 and blue LED 4b, to the output b of decoder driver 24, and, via blue LED 4c, to the output c of decoder driver 24. As a result of blending light of red and blue colors in each segment, segments b and c illuminate in substantially purple color.

To illuminate display element 43 in blue-green color, the color control input BG is raised to a high logic level, while all remaining color control inputs are maintained at a low logic level. As a result, the outputs of OR gates 61b and 61c rise to a high logic level, thereby causing the outputs of buffers 62b and 62c to rise to a high logic level. The current flows from the output of buffer 62b, via green bus 6 and green LED 3b, to the output b of decoder driver 24, and, via green LED 3c, to the output c of decoder driver 24. The current also flows from the output of buffer 62c, via blue bus 7 and blue LED 4b, to the output b of decoder driver 24, and, via blue LED 4c, to the output c of decoder driver 24. As a result of blending light of green and blue colors in each segment, segments b and c illuminate in substantially blue-green color.

To illuminate display element 43 in white color, the color control input W is raised to a high logic level, while all remaining color control inputs are maintained at a low logic level. As a result, the outputs of OR gates 61a, 61b, and 61c rise to a high logic level, thereby causing the outputs of respective buffers 62a, 62b, and 62c to rise to a high logic level. The current flows from the output of buffer 62a, via red bus 5 and red LED 2b, to the output b of decoder driver 24, and, via red LED 2c, to the output c of decoder driver 24. The current also flows from the output of buffer 62b, via green bus 6 and green LED 3b, to the output b of decoder driver 24, and, via green LED 3c, to the output c of decoder driver 24. The current also flows from the output of buffer 62c, via blue bus 7 and blue LED 4b, to the output b of decoder driver 24, and, via blue LED 4c, to the output c of decoder driver 24. As a result of blending light of red, green, and blue colors in each segment, segments b and c illuminate in substantially white color.

Since the outputs of decoder driver 24 may be overloaded by driving a triad of LEDs in parallel in display element 43, rather than a single LED in a monochromatic display, it would be obvious to employ suitable buffers to drive respective color display segments (not shown).

To illustrate how the present invention can be utilized in a multi-element variable color display configuration, in FIG. 19 is shown a detail of the interconnection in a 2-primary color 4-digit display having display segments 1a, 1b, 1c, and 1d arranged in a 7-segment font. The color control inputs R, Y, and G of color controls 52a, 52b, 52c, and 52d of all display elements 46a, 46b, 46c, and 46d are interconnected, respectively, and enable inputs E1, E2, E3, and E4 are used to control the conditions of respective display elements 46a, 46b, 46c, and 46d. A high logic level at the enable input E extinguishes the particular display element 46a, 46b, 46c, or 46d; a low logic level therein illuminates display element 46a, 46b, 46c, or 46d in a color determined by the instant conditions of the color control inputs R, Y, and G.

In FIG. 20 is shown a like detail of the interconnection in a 3-primary color 4-digit display having display segments 1a, 1b, 1c, and 1d arranged in a 7-segment font. Similarly, the color control inputs B, P, BG, G, Y, W, and R of color controls 53a, 53b, 53c, and 53d of all display elements 47a, 47b, 47c, and 47d are interconnected, and the conditions of respective display elements 47a, 47b, 47c, and 47d are controlled by enable inputs E1, E2, E3, and E4. A high logic level at the enable input E extinguishes the particular display element 47a, 47b, 47c, or 47d; a low logic level therein illuminates display element 47a, 47b, 47c, or 47d in a color determined by the instant conditions of the color control inputs B, P, BG, G, Y, W, and R.

The exemplary color control circuits described herein will cooperate equally well with a multi-element variable color display constructed either in common cathodes or in common anodes configuration.

The enable inputs E1, E2, E3, E4 may be utilized to control the variable color multi-digit display in a multiplexed configuration, wherein the color codes for the display digits are presented in a sequence, one at a time, at a relatively fast rate, while the particular display digit is enabled.

In FIG. 21 is shown a block diagram of a signal converter for developing color control logic signals for 2-primary color display. The signal converter 85a accepts at its input voltage from a variable analog voltage source 11 and develops at its outputs color control logic signals R, Y, G, having relation to the magnitude of instant input analog voltage, for controlling the color of variable color display element 42, shown in FIGS. 11 and 15, in accordance with the magnitude of input voltage.

In FIG. 22 is shown a block diagram of a like signal converter for developing color control logic signals for 3-primary color display. The signal converter 85b accepts at its inputs voltage from source 11 and develops output color control logic signals B, P, BG, G, Y, W, R, related to the magnitude of instant input analog voltage, for controlling the color of variable color display element 43, shown in FIGS. 12 and 16, in accordance with the magnitude of input voltage.

In FIG. 23, the output voltage of variable analog voltage source 11 is applied to interconnected inputs of two analog comparators 82a, 82b, in a classic `window` comparator configuration. When the voltage developed by source 11 is lower than the low voltage limit Vlo, set by a potentiometer 92a, the output of comparator 82a drops to a low logic level, thereby forcing the output of inverter 65a to rise to a high logic level, to activate the color control logic input Y, to thereby illuminate display element 42, shown in FIGS. 11 and 15, in yellow color.

When the voltage developed by source 11 is higher than the high voltage limit Vhi, set by a potentiometer 92b, the output of comparator 82b drops to a low logic level, thereby forcing the output of inverter 65b to rise to a high logic level, to activate the color control logic input R, to thereby illuminate display element 42 in red color. When the voltage developed by source 11 is between the low voltage limit Vlo and high voltage limit Vhi, the outputs of comparators 82a, 82b rise to a high logic level, thereby causing the output of AND gate 66 to rise to a high logic level, to activate the color control logic input G, to thereby illuminate display element 42 in green color.

FIG. 24 is a graph depicting the relationship between the input voltage of the comparator circuit shown in FIG. 23 and the color of the display element shown in FIG. 11. The display element illuminates in yellow color for the input voltage lower than the limit Vlo, in green color for the input voltage between the limits Vlo and Vhi, and in red color for the input voltage higher than the limit Vhi. In FIG. 25, the output voltage of variable analog voltage source 11 is applied to interconnected `+` inputs of six analog comparators 82c, 82d, 82e, 82f, 82g, 82h, connected in a well known `multiple aperture window` configuration. There are six progressively increasing voltage limits V1 to V6, set by respective potentiometers 92c to 92h. The outputs of comparators 82c to 82h are respectively connected, via inverters 65c to 65h, to the inputs I1 to I7 of a priority encoder 67. Each of the inputs I1 to I7 has assigned a certain priority (from I1 being the lowest priority progressively to I7 being the highest one). The priority encoder 67 develops at its outputs 00, 01, 02 a code identifying the highest priority input activated. The outputs of encoder 67 are respectively connected, via inverters 65j to 65m, to the inputs A0, A1, A2 of a 3-to-8 line decoder 68, to decode the outputs of encoder 67 into seven mutually exclusive active logic low outputs Y1 to Y7. The outputs Y1 to Y7 are respectively connected, via inverters 65p to 65v, to the color control logic inputs B, P, BG, G, Y, W, R of display element 43 shown in FIGS. 12 and 16.

When the output voltage of source 11 is lower than the lowest voltage limit V1, the output of comparator 82c drops to a low logic level, thereby activating the input I1 of priority encoder 67. The code 110 developed at the outputs 00, 01, 02 is inverted by inverters 65j to 65m to yield the code 001 which produces a low logic level at the output Y1, to force, via inverter 65p, the color control input B to a high logic level for causing display element 43 to illuminate in blue color.

When the output voltage of the source 11 is between the adjacent voltage limits, e. g., V4 and V5, the output of comparator 82f rises to a high logic level, thereby activating the input I5 of priority encoder 67. The code 100 developed at the inputs of decoder 68 produces a high logic level at the color control logic input Y, and display element 43 illuminates in yellow color.

FIG. 26 is a graph depicting the relationship between the input voltage of the comparator circuit shown in FIG. 25 and the color of display element 42 shown in FIG. 12. The display element illuminates in blue color for the input voltage lower than the limit V1, in purple color for the input voltage between the limits V1 and V2, in blue-green color for the input voltage between the limits V2 and V3, in green color for the input voltage between the limits V3 and V4, in yellow color for the input voltage between the limits V4 and V5, in white color for the input voltage between the limits V5 and V6, and in red color for the input voltage higher than the limit V6.

It would be obvious to those having ordinary skill in the art, in the view of this disclosure, that the color sequences could be readily changed by differently interconnecting the outputs of the comparator circuit with the color control logic inputs of display element 43.

CONTINUOUSLY VARIABLE COLOR CONVERTER

FIG. 27 is a block diagram of a 2-LED continuously variable color display system, which includes a device 10 for developing electric signals and 2-LED color converter 57 for controlling red bus 5 and green bus 6, respectively, of 2-LED variable color display element 42 in accordance with the electric signals.

FIG. 28 is a block diagram of a 3-LED continuously variable color display system which differs from the like system shown in FIG. 27 in that a 3-LED color converter circuit 58 is utilized to control red bus 5, green bus 6, and blue bus 7, respectively, of 3-LED variable color display element 43, in accordance with the electric signals developed by device 10.

The display system shown in FIG. 29 utilizes a scaling circuit 80a which scales input analog voltage levels to a voltage range suitable for an A/D converter 74a, which in turn develops at its outputs a digital code having relation to the value of the input analog voltage. The output lines of A/D converter 74a are connected to the address inputs of a memory 76 having a plurality of addressable locations which contain data indicating the portions of red color for several different values of the input analog voltage. The output data of memory 76 are applied to the inputs of a color converter 57 which will develop control signals for red bus 5 and green bus 6, respectively, of variable color display element 42.

The display system shown in FIG. 30 utilizes a scaling circuit 80b and an A/D converter 74b for converting the instant value of an input analog voltage to a digital code. The outputs of A/D converter 74b are connected, in parallel, to the address inputs of memory 76a, which contains data indicating the portions of red color, to the address inputs of memory 76b, which contains data indicating the portions of green color, and to the address inputs of memory 76c, which contains data indicating the portions of blue color. The output data of memory 76a are applied to red color converter 59a which will develop control signals for red bus 5 of variable color display element 43. The output data of memory 76b are applied to green color converter 59b which will develop control signals for green bus 6 of display element 43. The output data of memory 76c are applied to blue color converter 59c which will develop control signals for blue bus 7 of display element 43.

FIG. 31 is a schematic diagram of a scaling circuit capable of shifting and amplifying the input voltage levels. The circuit utilizes two operational amplifiers 81a and 81b in a standard inverting configuration. The amplifier 81a is set for a unity gain by using resistors 90a and 90b of equal values; potentiometer 92a is adjusted to set a desired offset voltage. The amplifier 81b sets the gain by adjusting feedback potentiometer 92b to a desired value with respect to resistor 90c. As a result, an input voltage, which may vary between arbitrary limits Vlow and Vhigh, may be scaled and shifted to the range between 0 Volts and 9.961 Volts, to facilitate the use of a commercially available A/D converter.

FIG. 32 is a schematic diagram of an A/D (analog-to-digital) converter 75 which is capable of converting input analog voltage, applied via resistor 90e to its input Vin, to 8-bit digital data for addressing a memory 77. The conversion may be initiated from time to time by applying a short positive pulse 99a to the Blank and Convert input B&C. A/D converter 75 will thereafter perform a conversion of the instant input voltage to 8-bit data indicative of its value. When the conversion is completed, the Data Ready output DR drops to a low logic level, thereby indicating that the data are available at the outputs Bit 1 to Bit 8, which are directly connected to respective address inputs A0 to A7 of memory 77. When the DR output drops to a low logic level, the Chip Select input CS of memory 77 is activated, memory 77 is enabled, and the data, residing at the address selected by the instant output of A/D converter 75, will appear at its data outputs D0 to D7.

The description of the schematic diagram in FIG. 33 should be considered together with its accompanying timing diagram shown in FIG. 34. A clock signal 99b of a suitable frequency (e. g., 10 kHz), to provide a flicker-free display, is applied to the Clock Pulse inputs CP of 8-bit binary counters 71e and 71f to step them down. At the end of each counter cycle, which takes 256 clock cycles to complete, the Terminal Count output TC of counter 71e drops to a low logic level for one clock cycle, to thereby indicate that the lowest count was reached. The negative pulse 99c at the TC output of counter 71e, which is connected to the Parallel Load input PL of counter 71f, causes the instant data at the outputs of memory 76 to be loaded into counter 71f. The data at memory 76 represent the portion of red color; the portion of green color is complementary. The rising edge of the TC pulse 99c triggers flip-flop 73 into its set condition wherein its output Q rises to a high logic level.

The counter 71f will count down, from the loaded value, until it reaches zero count, at which moment its TC output drops to a low logic level. The negative pulse at the TC output of counter 71f, which is connected to the Clear Direct input CD of flip-flop 73, causes the latter to be reset and to remain in its reset condition until it is set again at the beginning of the next 256-count cycle. It is thus obvious that the Q output of flip-flop 73 is at a high logic level for a period of time proportional to the data initially loaded into counter 71f. The complementary output Q is at a high logic level for a complementary period of time.

The Q and Q outputs of flip-flop 73 are connected to red bus 5 and green bus 6, respectively, via suitable buffers 63a and 63b, shown in detail in FIG. 11, to respectively energize red bus 5 and green bus 6 for variable time periods, depending on the data stored in memory 76.

By referring now, more particularly, to the timing diagram shown in FIG. 34, in which the waveforms are compressed to facilitate the illustration, the EXAMPLE 1 considers the memory data `FD`, in a standard hexadecimal notation, to generate light of substantially red color. At the beginning of the counter cycle, pulse 99c loads data `FD` into counter 71f. Simultaneously, flip-flop 73 is set by the rising edge of pulse 99c. The counter 71f will be thereafter stepped down by clock pulses 99b, until it reaches zero count, 2 clock cycles before the end of the counter cycle. At that instant a short negative pulse 99d is produced at its output TC to reset flip-flop 73, which will remain reset for 2 clock cycles and will be set again by pulse 99c at the beginning of the next counter cycle, which will repeat the process. It is readily apparent that flip-flop 73 was set for 254 clock cycles, or about 99% of the time, and reset for 2 clock cycles, or about 1% of the time. Accordingly, red bus 5 of display element 42 is energized for about 99% of the time, and green bus 6 is energized for the remaining about 1% of the time. As a result, display element 42 illuminates in substantially red color.

The EXAMPLE 2 considers the memory data `02` (HEX) to generate light of substantially green color. At the beginning of the counter cycle, data `02` are loaded into counter 71f, and, simultaneously, flip-flop 73 is set. The counter 71f will count down and will reach zero count after 2 clock cycles. At that instant it produces at its output TC a negative pulse 99e to reset flip-flop 73. It is readily apparent that flip-flop 73 was set for 2 clock cycles, or about 1% of the time, and reset for 254 clock cycles, or about 99% of the time. Accordingly, red bus 5 of display element 42 is energized for about 1% of the time, and green bus 6 is energized for the remaining about 99% of the time. As a result, display element 42 illuminates in substantially green color.

The EXAMPLE 3 considers the memory data `80` (HEX) to generate light of substantially yellow color. At the beginning of the counter cycle, data `80` are loaded into counter 71f, and, simultaneously, flip-flop 73 is set. The counter 71f will count down and will reach zero count after 128 clock cycles. At that instant it produces at its output TC a negative pulse 99f to reset flip-flop 73. It is readily apparent that flip-flop 73 was set for 128 clock cycles, or about 50% of the time, and reset for 128 clock cycles, or about 50% of the time. Accordingly, red bus 5 of display element 42 is energized for about 50% of the time, and green bus 6 is energized for the remaining about 50% of the time. As a result of blending substantially equal portions of red and green colors, display element 42 illuminates in substantially yellow color.

The description of the schematic diagram of a 3-LED color converter in FIG. 19 should be considered together with its accompanying timing diagrams shown in FIGS. 20 and 21. A clock signal 99b is applied to the CP inputs of counters 71d, 71a, 71b, and 71c to step them down. Every 256 counts a negative pulse 99c is generated at the TC output of counter 71d, to load data into counters 71a, 71b, and 71c from respective memories 76a, 76b, and 76c, and to set flip-flops 73a, 73b, and 73c. The data in red memory 76a represent the portions of red color, the data in green memory 76b represent the portions of green color, and the data in blue memory 76c represent the portions of blue color to be blended.

The counters 71a, 71b, and 71c will count down, from the respective loaded values, until zero counts are reached. When the respective values of the loaded data are different, the length of time of the count-down is different for each counter 71a, 71b, and 71c. When a particular counter 71a, 71b, or 71c reaches zero count, its TC output momentarily drops to a low logic level, to reset its associated flip-flop (red counter 71a resets its red flip-flop 73a, green counter 71b resets its associated green flip-flop 73b, and blue counter 71c resets its associated blue flip-flop 73c). Eventually, all three flip-flops 73a, 73b, and 73c will be reset. The Q outputs of flip-flops 73a, 73b, and 73c are connected to red bus 5, green bus 6, and blue bus 7, respectively, via suitable buffers 62a, 62b, and 62c, as shown in FIG. 8, to respectively energize red bus 5, green bus 6, and blue bus 7 for variable periods of time.

By referring now more particularly to the timing diagram shown in FIGS. 20 and 21, the EXAMPLE 4 considers red memory data `80`, green memory data `00`, and blue memory data `80`, all in hexadecimal notation, to generate light of substantially purple color. At the beginning of the counter cycle, pulse 99c simultaneously loads data `80` from red memory 76a into red counter 71a, data `00` from green memory 76b into green counter 71b, and data `80` from blue memory 76c into blue counter 71c. The counters 71a, 71b, and 71c will be thereafter stepped down. The red counter 71a will reach its zero count after 128 clock cycles; green counter 71b will reach its zero count immediately; blue counter 71c will reach its zero count after 128 clock cycles.

It is readily apparent that red flip-flop 73a was set for 128 clock cycles, or about 50% of the time, green flip-flop 73b was never set, and blue flip-flop 73c was set for 128 clock cycles, or about 50% of the time. Accordingly, red bus 5 of display element 43 is energized for about 50% of the time, green bus 6 is never energized, and blue bus 7 is energized for about 50% of the time. As a result of blending substantially equal portions of red and blue colors, display element 43 illuminates in substantially purple color.

The EXAMPLE 5 considers red memory data `00`, green memory data `80`, and blue memory data `80`, to generate light of substantially blue-green color. At the beginning of the counter cycle, data `00` are loaded into red counter 71a, data `80` are loaded into green counter 71b, and data `80` are loaded into blue counter 71c. The red counter 71a will reach its zero count immediately, green counter 71b will reach its zero count after 128 clock periods, and so will blue counter 71c.

The red flip-flop 73a was never set, green flip-flop 73b was set for 128 clock pulses, or about 50% of the time, and so was blue flip-flop 73c. Accordingly, green bus 6 of display element 43 is energized for about 50% of the time, and so is blue bus 7. As a result, display element 43 illuminates in substantially blue-green color.

The EXAMPLE 6 considers red memory data `40`, green memory data `40`, and blue memory data `80`, to generate light of substantially cyan color. At the beginning of the counter cycle, the data `40` are loaded into red counter 71a, data `40` are loaded into green counter 71b, and data `80` are loaded into blue counter 71c. The red counter 71a will reach its zero count after 64 clock cycles, and so will green counter 71b. The blue counter 71c will reach its zero count after 128 clock cycles.

The red flip-flop 73a was set for 64 clock cycles, or about 25% of the time, and so was green flip-flop 73b. The blue flip-flop 73c was set for 128 clock cycles, or about 50% of the time. Accordingly, red bus 5 and green bus 6 of display element 43 are energized for about 25% of the time, and blue bus 7 is energized for about 50% of the time. As a result of blending about 50% of blue color, 25% of red color, and 25% of green color, display element 43 illuminates in substantially cyan color.

The EXAMPLE 7 considers red memory data `80`, green memory data `40`, and blue memory data `40`, to generate light of substantially magenta color. At the beginning of the counter cycle, the data `80` are loaded into red counter 71a, data `40` are loaded into green counter 71b, and data `40` are loaded into blue counter 71c. The red counter 71a will reach its zero count after 128 clock cycles, green counter 71b will reach its zero count after 64 clock cycles, and so will blue counter 71c.

The red flip-flop 73a was set for 128 clock cycles, or about 50% of the time, green flip-flop 73b and blue flip-flop 73c were set for 64 clock cycles, or about 25% of the time. Accordingly, red bus 5 of display element 43 is energized for about 50% of the time, green bus 6 and blue bus 7 are energized for about 25% of the time. As a result, display element 43 illuminates in substantially magenta color.

By referring now more particularly to FIGS. 38 and 39, which are graphic representations of TABLES 1 and 2, respectively, the data at each memory address are digital representation of the portion of the particular primary color. All examples consider an 8-bit wide PROM (Programmable Read Only Memory). However, the principles of the invention could be applied to other types of memories.

In FIG. 38, RED PORTION indicates the portion of red primary color; GREEN PORTION indicates the portion of green primary color. The RED PORTION for a particular memory address was calculated by dividing the actual value of data residing at that address by the maximum possible data `FF` (HEX). The GREEN PORTION for the same memory address is complementary; it was obtained by subtracting the calculated value of the RED PORTION from number 1.0.

In FIG. 38 is shown the characteristic of a 2-primary color converter, defined in TABLE 1, for developing color variable in steps: pure green for input voltages less than 0.625 V, substantially yellow for voltages between 1.25 V and 1.875 V, pure red for voltages between 2.5 V and 3.125 V, and of intermediate colors therebetween, this sequence being repeated three times over the voltage range.

In FIG. 39, RED PORTION indicates the portion of red primary color; GREEN PORTION indicates the portion of green primary color; BLUE PORTION indicates the portion of blue primary color. The RED PORTION for a particular memory address was calculated by dividing the value of red data residing at such address by the maximum possible data `FF` (HEX). Similarly, the GREEN PORTION for that memory address was obtained by dividing the value of green data by `FF` (HEX). The BLUE PORTION was obtained by dividing the value of blue data by `FF` (HEX).

In FIG. 39 is shown the characteristic of 3-primary color converter, defined in TABLE 2, for developing color continuously variable from pure red, through substantially orange and yellow, pure green, pure blue, to substantially purple, in a rainbow-like fashion.

In the examples of the characteristics of color converters shown in TABLE 1 and TABLE 2, the data values stored in red memory 76a, green memory 76b, and blue memory 76c are so designed that the sums of the red data, green data, and blue data are constant for all memory addresses, to provide uniform light intensities for all colors. It is further contemplated that data stored in red memory 76a, green memory 76b, and blue memory 76c may be modified in order to compensate for different efficiencies of red, green, and blue LEDs. By way of an example, data values for a low efficiency LED may be proportionally incremented such that the time of energization is proportionally increased, to effectively provide equal luminances for LEDs of unequal efficiencies.

With reference to FIG. 40 there is shown the ICI (International Committee on Illumination) chromaticity diagram designed to specify a particular color in terms of x and y coordinates. Pure colors are located along the horseshoe-like periphery. Reference numbers along the periphery indicate wavelength in nanometers. When relative portions of three primary colors are known, the color of light produced by blending their emissions can be determined by examining the x and y values of ICI coordinates.

DIGITAL MULTIMETER

FIG. 41 is a generalized block diagram of a multimeter with variable color digital display which includes a multimeter 101 for measuring values of a QUANTITY 1, digital decoder driver 21 for converting the output data of multimeter 101 to a displayable code, and variable color digital display 40 for indicating the measured values in digital format. The invention resides in the addition of a color converter circuit 55 for converting values of a QUANTITY 2 to color control signals for controlling the color of display 40. The display 40 thus simultaneously indicates values of the QUANTITY 1, in digital format, and values of the QUANTITY 2, in variable color.

FIG. 42 is a generalized block diagram of a like multimeter system with a multiplexed variable color digital display 41, which differs from the diagram shown in FIG. 41 in that the multimeter 102 develops at its outputs multiplexed signals to directly drive display 41.

A digital multimeter shown in a block diagram configuration in FIG. 43 is capable of selectively setting certain of its external controls by an external control selector 121a. The invention resides in the addition of associated color selector 121b for causing variable color digital display 40 to illuminate in a color corresponding to the selected external control. The measurements performed with different external controls may be displayed in respectively different colors. The selectors 121a, 121b may include relays, mechanical switches, electronic and optical elements, devices for executing program of instructions, and the like. The association between the selectors 121a and 121b may be, in its simplest form, a direct coupling, whereby the selector 121b is always in the same position as the selector 121a, or a more sophisticated association in space, time, hardware, and software. The external controls may comprise measurement modes, such are local, remote, 2-wire, and 4-wire; measurement functions, such are DC voltage, AC voltage, DC current, AC current, resistance, capacitance, and inductance; measurement ranges for selectively scaling measured signals, and the like.

In FIG. 44 is shown a block diagram of a like digital multimeter capable of selectively setting certain of its internal measurement controls by an internal control selector 121a. The associated color selector 121b causes display 40 to illuminate in a color corresponding to the selected internal control, such that the measurements performed with different internal controls may be displayed in respectively different colors. The internal controls may comprise measurement modifiers, such are single, continuous, synchronous, and asynchronous triggering, sample rate, filter, offset, external reference, and scaling; measurement methods, units, and the like.

FIG. 45 is a block diagram of a digital multimeter with measurement quantity selection. By way of an example, when the quantity selector 121a is in its second position, thereby selecting the QUANTITY 2 to the input of digital multimeter 103, the associated color selector 121b is also in its second position, thereby applying the control voltage to the color control input C2, to cause the measured values of the QUANTITY 2 to be indicated on display 40 in the color C2. The measurements of different quantities may be indicated in respectively different colors.

FIG. 46 is a block diagram of a digital multimeter with input location selection. By way of an example, when the location selector 121a is in its third position, thereby selecting for the input of multimeter 103 signals from the LOCATION 3, the associated color selector 121b is also in its third position, thereby applying the control voltage to the color control input C3, to cause the measured values from the LOCATION 3 to be indicated on display 40 in the color C3. The measurements from different locations may be indicated in respectively different colors.

In FIG. 47 is shown an exemplary simplified schematic diagram of a digital multimeter for selectively measuring values of several different quantities from outputs of a temperature transducer 172, which converts temperature to voltage, pressure transducer 173, which converts atmospheric pressure to voltage, and physiological transducer 174, which converts physiological information to voltage. The term transducer, as used throughout the description of the invention, is used in its widest sense so as to include every type of a device for performing a conversion of one form of energy to another. The principles of the invention may be applied to various displacement, motion, force, pressure, sound, flow, temperature, humidity, weight, magnetic, and physiological transducers, and the like. When switch 123g is in its first position, thereby selecting temperature transducer 172, digital voltmeter 108 measures the output voltage of transducer 172, which is proportional to ambient temperature, and display 48 indicates the measured temperature in digital format. The associated switch 123h is also in its first position, thereby connecting the control voltage +VCC to the color control input C1 of the color control circuit 42, to cause the display 48 to illuminate in the color C1. When switch 123g is in its second position, thereby selecting pressure transducer 173, display 48 indicates the measured atmospheric pressure in digital format and in the color C2. When switch 123g is in its last position, thereby selecting physiological transducer 174, display 48 indicates the measured physiological information, such as blood pressure, heart beat, and the like, in digital format and in the color Cn. Measured values of different quantities are thus displayed in respectively different colors.

In FIG. 48 is shown an exemplary simplified schematic diagram of a digital multimeter capable of measuring signals from seven different locations and of indicating the measured results in seven different colors, respectively. The outputs Q0, Q1, Q2 of a 4-bit binary counter 162b, which may be from time to time incremented by a clock pulse, are connected, in parallel, to the address inputs A, B, C of analog multiplexers 147a, 147b, respectively, to cause the multiplexer 147a to internally route signals from its selected input, e. g., Y1, to its output Y, and, simultaneously, to apply the control voltage +VCC from the terminal Y of multiplexer 147b, via its selected terminal, e. g., Y1, to one of the color control inputs B to R. The measured signals from the selected location are indicated on display 40 in digital format and in a color unique to the selected location. The indicated color sequences are merely exemplary; it would be obvious to devise other color sequences by differently interconnecting the terminals Y1 to Y7 of multiplexer 147b with the color control inputs.

In FIG. 49 is shown a simplified schematic diagram of an AC digital voltmeter for selectively measuring an RMS (Root Mean Square) or MAV (Mean Average Value) of a measured waveform. An RMS measurement provides a power content of the measured signal, as will be more fully explained later, for a waveform of any shape. Since the MAV measured value may differ from the RMS value for certain waveform shapes, it would be desirable to know which measurement method is employed. A switch 123i selects either the output of RMS converter 181 or the output of the precision rectifier circuit, consisting of an op amp 159a, resistors 124x, 124y, 124z and diodes 128a, 128b, to the input of digital voltmeter 108. An associated switch 123j selects one of the color control inputs C1, C2, in accordance with the selection of the measurement method. The display 48 indicates the magnitude of the measured AC waveform in digital format and in a color unique to the selected measurement method.

In FIG. 50 is shown a simplified schematic diagram of a digital thermometer which can selectively measure temperature in the Kelvin, Celsius, or Fahrenheit scale, by connecting the output of one of temperature transducers 177, 178, 179, via a switch 123m, to the input of digital voltmeter 108. An associated switch 123n applies the control voltage +VCC to one of the color control inputs C1, C2, C3, of the color control circuit 52, to thereby illuminate display 48 in a color unique to the selected temperature scale. The output voltage of Kelvin temperature transducer 177 is linearly proportional to temperature in the Kelvin scale. The output voltage of like Celsius temperature transducer 178 is linearly proportional to temperature in the Celsius scale. The output voltage of like Fahrenheit temperature transducer 179 is linearly proportional to temperature in the Fahrenheit scale.

In FIG. 51 is shown a simplified schematic diagram of a digital ampermeter with variable color range indication. The precision shunt resistors 126a, 126b, 126c, 126d, 126e, connected in series, convert measured current to voltage, which is applied, via a resistor 125f of suitable value, to the input terminal of digital voltmeter 108. The current range is selectable by a rotary switch 123a, in a manner well known to those skilled in the art. The invention resides in the addition of a second rotary switch 123b, associated with the switch 123a such that both switches are always in the same position, to connect the reference voltage +VCC to the selected one of the color control inputs, in accordance with the selected current range. The remaining color control inputs are tied to ground via suitable pull down resistors 125a, 125b, 125c, 125d, 125e. By way of an example, display 40 may indicate measured current values on the 0.2 mA range in blue color, on 2 mA range in purple color, on 20 mA range in green color, on 200 mA range in yellow color, and on 2 A range in red color.

In FIG. 52 is shown a simplified schematic diagram of a digital voltmeter with variable color range indication. The precision voltage attenuating resistors 126f, 126g, 126h, 126i, 126j are connected in series, and the voltage range is selected by a rotary switch 123c, in a manner well understood by those skilled in the art. The invention resides in the addition of a second rotary switch 123d, associated with the switch 123c, to apply the reference voltage +VCC to the selected color control input. By way of an example, display 40 may indicate measured values on the 0.2 V range in white color, on 2 V range in yellow color, on 20 V range in green color, on 200 V range in blue-green color, and on 2000 V range in red color.

In FIG. 53 is shown a simplified schematic diagram of a digital ohmmeter with variable color range indication. The precision standard resistors 126k, 126m, 126n, 126p, 126r, selectable by a rotary range switch 123e, are connected such that the selected one of the standard resistors is in series with the measured resistance Rx, in a well known ratiometric arrangement. The invention resides in the addition of a second switch 123f, associated with the switch 123e, to connect the reference voltage +VCC to the selected one of the color control inputs, in accordance with the selected resistance range. By way of an example, display 40 may indicate measured resistance values on the 0.1 k range in yellow color, on 1 k range in green color, on 10 k range in blue color, on 100 k range in purple color, and on 1 M range in red color.

The examples of range and precision resistor values shown in FIGS. 51, 52, 53 should be considered merely as exemplary. Although the switches 123 are shown as rotary switches, they may, alternatively, be of any other type, such are pushbutton switches and relay contacts. Another modification envisions that only certain of the display digits may change color in accordance with the measurement range, while the remaining display digits may change color in accordance with a different quantity. It is readily apparent that the principles of the invention may be effectively applied to autoranging multimeters.

In FIG. 54 is shown a detail of the multimeter of FIGS. 51, 52, 53 which includes a DVM chip 108 capable of converting analog voltage applied to its inputs HI and LO into signals for directly driving respective segments of a 31/2 digit 7-segment variable color display 48. The color control 50 causes display 48 to illuminate in a selected color, as described previously.

Commercially known digital multimeters are capable of indicating negative measured results, by displaying a small negative sign at the most significant digit, and positive measured results, usually by not displaying the minus sign. When a series of measurements is performed, it is difficult to distinguish between the positive and negative measurement results displayed on a long character string, particularly when the measurements are performed at a relatively fast rate. In FIG. 55 is shown how this problem may be effectively solved by displaying positive and negative measurement results in respectively different colors on a 31/2 digit common cathodes variable color display 48, which is capable of displaying a minus sign by illuminating the segment g in the most significant digit. The polarity output POL of digital voltmeter 108 is directly connected to the color control input R, and, via an inverter 151a, to the color control input G, of the color control circuit 52. When the POL output is at a low logic level, to indicate that the displayed number is positive, the minus sign is extinguished. A low logic level at the POL output forces the output of the inverter 151a to rise to a high logic level, to activate the color control input G, to thereby illuminate display 48 in green color. When the POL output rises to a high logic level, to indicate that the displayed number is negative, the minus sign is illuminated. A high logic level at the POL output activates the color control input R, to thereby illuminate display 48 in red color. It would be obvious, in the view of the present disclosure, to devise other color combinations.

The description of a variable color digital display system shown in FIG. 56, which is capable of emphasizing the position of a decimal point in a string of digits, should be considered together with its accompanying timing diagram shown in FIG. 57. The display system, which in its exemplary embodiment utilizes eight single-digit variable color displays 46a to 46h, which are only partially shown, is capable of detecting the position of decimal point in a string of displayed digits and of displaying all digits that precede the decimal point in a first color and all digits that follow the decimal point in a second color. The decimal point outputs DP of common-cathodes 7-segment decoders 23a to 23h, which may receive displayable data in a conventional manner (not shown), are continuously scanned in a sequence by a multiplexer 146 which is incremented by a counter 162d driven by clock 199j of a suitable frequency. When an active high DP output is detected on certain of the decoders 23a to 23h, the inverting output W of multiplexer 146, which is connected to the set direct input SD of DP flip-flop 138j, drops to a low logic level 199n, to force the latter to its set condition. The Q output of DP flip-flop 138j, which is connected to the D inputs of all flip-flops 138b to 138h, rises to a high logic level for the remaining time of the scanning cycle, to thereby indicate, as may be best observed in FIG. 57 in the line designated F--F 138j Q OUTPUT at waveform 199p, the position of the detected decimal point in reference to the scanning cycle. A decoder 166 is incremented synchronously with the multiplexer 146, and, as a result, its outputs Y0 to Y7 are sequentially driven to a low logic level, to trigger in a sequence flip-flops 138b to 138h to states determined by the conditions of their D inputs, respectively, at the time of triggering, as may be best observed in FIG. 57 in the lines designated DEC 166 OUTPUTS Y0 to Y7 at waveforms 199a to 199h. All flip-flops 138b to 138h, which were triggered before the decimal point was located during the scanning cycle, are triggered to their reset states, while all remaining flip-flops 138b to 138h, which were triggered after the decimal point was located, are triggered to their set states. The Y7 output of the decoder 166 is connected to the clear direct input CD of the DP flip-flop 138j, to force the latter to its reset condition at the end of each scanning cycle. The outputs Q and Q of flip-flops 138b to 138h are respectively connected to color control inputs R and G of the color control circuits 52b to 52h, to thereby cause all display digits 46b to 46h that precede the instant decimal point to be illuminated in green color, and all remaining display digits that follow the decimal point to be illuminated in red color. It would be obvious that other color combinations may be devised.

The display system shown in FIG. 58 is capable of detecting the presence or absence of decimal point in the displayed digital string, and accordingly of displaying digital strings with decimal point (decimal numbers) in a first color, and digital strings without decimal point (integers) in a different color. The decimal point outputs DP of all common-cathode 7-segment decoders 23a to 23h are respectively connected to the inputs of an OR gate 154. When decimal point is present in the displayed digital string, the appropriate DP output rises to a high logic level, thereby forcing the non-inverting output of OR gate 154, which is connected to interconnected color control inputs R of all color control circuits 52a to 52h, to rise to a high logic level, to thereby cause all displays 46a to 46h to illuminate in red color. When no decimal point is detected in the displayed digital string, the inverting output of OR gate 154, which is connected to interconnected color control inputs G of all color control circuits 52a to 52h, rises to a high logic level, to thereby cause all displays 46a to 46h to illuminate in green color.

In FIG. 59 is shown a block diagram of a variable color digital display system for selectively indicating output values of seven digital devices 12a to 12g in digital format and in respectively different colors. The outputs of digital devices 12a to 12g are respectively connected to the inputs I1 to I7 of a digital multiplexer 146b, which is addressed by a counter 161c. Displayable digital data are routed from one of the multiplexer's inputs, selected by the instant output code of counter 161c, to its output Z and to variable color digital display element 43, to be displayed thereon in digital format. The counter 161c simultaneously addresses color decoder 165a, to activate one of seven color control inputs B, P, BG, G, Y, W, R of color control circuit 53, in accordance with the selected input of multiplexer 146b. By way of an example, when the counter's output code 010 (binary) is applied to the address inputs of multiplexer 146b, the input I2 is selected, and data from digital device 12b are indicated on display element 43 in digital format. Simultaneously, the counter's output code causes the output Y2 of decoder 165a to be active, thereby activating the color control input P, to cause display element 43 to illuminate in purple color. Digital devices 12a to 12g may include certain of those disclosed earlier.

In FIG. 60 is shown an expanded block diagram of a variable color digital barometer with memory, for indicating measured values of atmospheric pressure in digital format and in a color depending on previous measured values. A scaling circuit consisting of op amps 159c, 159d and resistors 124a, 124b, 124c, 124d, 124e shifts and scales output voltage of a pressure transducer 176, which is linearly proportional to atmospheric pressure, such that voltage at the input of digital voltmeter 107 directly corresponds to the atmospheric pressure, either in milibars or in mm Hg, depending on the values of resistor 124e and V REF voltage. The digital voltmeter 107 converts the instant analog voltage at its input to a digital code which is simultaneously applied to variable color digital display 40, to be indicated thereon in digital format, and to the data input of a combined memory and comparator 144, to be stored therein from time to time. The invention resides in the addition of a color control circuit 50 for illuminating display 40 in a color depending on the result of comparison between the instant measured value of atmospheric pressure and previously stored one, to thereby indicate whether the atmospheric pressure is either rising, or falling, or remains unchanged. A three-decade counter 164, or other suitable device for keeping time, is incremented in regular intervals by a clock, and its DIGITS outputs indicate the instant count. A decoder 165b has its ADDRESS inputs connected, in a rather simplified manner, to the counter's DIGITS outputs and utilizes the counter's SELECT output as a strobe. As a result of continuous counting, at regular time intervals there will appear relatively short pulses 99m at the selected decoder's output Yn, which is connected to the LOAD input of memory and comparator 144, to load the instant output data of digital voltmeter 107 into memory 144. The comparator 144 effects a comparison of the data currently stored in its memory with the instant output data of digital voltmeter 107 and accordingly develops output signals LT (Less Than), EQ (Equal), and GT (Greater Than) The comparator's outputs LT, EQ, GT are respectively connected to the color control inputs R, Y, G of color control circuit 50, to cause display 40 to illuminate in red color when the comparator's output LT is active (atmospheric pressure is falling), in yellow color when the output EQ is active (atmospheric pressure is unchanged), and in green color when the output GT is active (atmospheric pressure is rising). The above description may serve as a background for consideration of more sophisticated barometric systems capable of comparing the instant measured values with values obtained by virtue of arithmetic and logic operations, such are average or peak values of previous measurements, and of displaying measured values in a variety of colors depending on the rate of increase or decrease of measured values.

In FIG. 61 is shown a block diagram of a digital multimeter 103 for making series of measurements in combination with a clock 148 for keeping time. The time signals developed by the clock circuit 148 are decoded by a suitable time decoder 168 and converted to color control signals C1, C2 to Cn. The values measured by the multimeter 103 are indicated on display 40 in digital format and in a color having relation to time.

FIG. 62 is a block diagram of a multimeter which includes a memory 131, containing a reference measured value, and a comparator 141. Measured values of input signal, which is applied to an input conditioning circuit 120, wherein it may be switched, scaled, attenuated, rectified, and filtered (not shown), are compared with the reference value stored in memory 131 and indicated on display 40 in digital format and in a color depending on the relationship between the measured value and the reference one. The memory 131 may include electronic storage elements, such are flip-flops, latches, RAMs, ROMs, and the like, and mechanical storage elements, such are binary switches or the like. When the instant measured value is less than the reference value, the output `<` of the comparator 141 is active, thereby activating the color control input C2 of the color control circuit 50, to illuminate display 40 in the color C2. When the instant measured value is greater than the reference one, the comparator's output `>` is active, and the measured value is displayed in the color C1. Alternatively, the instant measured value may be displayed in a color indicating its deviation, absolute or relative, from the reference value.

FIG. 63 is a block diagram of a multimeter which includes a memory 131a for storing a low measurement limit, memory 131b for storing a high measurement limit, and comparators 141a, 141b. The measured values are compared with the high and low measurement limits and are indicated on display 40 in digital format and in a color depending on the relationship between the measured value and the low and high measurement limits. When the measured value is lower than the low measurement limit, stored in memory 131a, the output `<` of the comparator 141a is active, thereby activating the color control input C3 of the color control circuit 50, to illuminate display 40 in the color C3. When the measurement value is higher that the high measurement limit, stored in memory 131b, the output `>` of comparator 141b is active, thereby activating the color control input C1, to illuminate display 40 in the color C1. When the measured value is higher than the low measurement limit and lower than the high measurement limit, the active outputs `>` of the comparator 141a and `<` of the comparator 141b are combined in a logic fashion by a logic circuit 150, thereby activating the color control input C2, to illuminate display 40 in the color C2.

FIG. 64 is a block diagram of a multimeter for making repeated measurements, which includes an A/D converter 106 and memory & comparator circuit 144. The instant measured value of the input signal, converted to digital format by the A/D converter 106, may be from time to time stored in memory 144, so that subsequent measurements could be compared with the stored values. The instant measured value is displayed on display 40 in digital format and in a color depending on the result of comparison with the value stored in the memory. When the instant measured value is less than that stored in the memory, the output LT (Less Than) of comparator 144 is active, thereby activating the color control input C3 of color control circuit 50, to display the measured value in the color C3. When the instant measured value is equal to that stored in the memory, the comparator output EQ (Equal) is active, thereby activating the color control input C2, to display the measured value in the color C2. When the instant measured value is greater than that stored in the memory, the comparator output GT (Greater Than) is active, thereby activating the color control input C1, to display the measured value in the color C1.

FIG. 65 is a block diagram of a multimeter for making a series of measurements and for comparing each measured value, by comparators 141a, 141b, with low and high measurement limits stored in memories 131a, 131b, respectively. An additional error memory 131c, which may include an error counter, and logic circuit 150a are provided for storing the number of measurement errors. The instant measured value is indicated on display 40 in digital format and in a color depending, firstly, on its relationship with the applicable low and high measurement limits, and, secondly, on the number of previous measurement errors. Various kinds of decisions may be made, by a logic circuit 150b, based on the contents of the error memory. The decisions may be as simple as merely to display the measurement results in the color C1 for no previous measurement errors and in the color C2 for some previous errors, or may involve sophisticated color selections based on the number of previous errors and total number of measurements, arrived at by virtue of arithmetic and logic operations.

In FIG. 66 is shown an exemplary simplified schematic diagram of the limit memory and limit comparator combination, generally shown in FIG. 65, for 8-bit measurement data (two BCD digits). The 8-bit data stored in a memory 132a, symbolizing the low measurement limit, are applied to respective inputs B0 to B7 of a digital comparator 143a; the 8-bit data stored in a like memory 132b, symbolizing the high measurement limit, are applied to respective inputs B0 to B7 of a comparator 143b. The 8-bit measurement data, having relation to the instant measured value, are applied to respective inputs A0 to A7 of both comparators 143a, 143b, interconnected in parallel. The comparators 143a, 143b effect a comparison between the measurement data and the instant low and high measurement limits and accordingly develop their output signals `<`, `=`, `>`. When the instant measurement data are less than the low measurement limit, the `<` output of the comparator 143a rises to a high logic level. When the instant measurement data are greater than the high measurement limit, the `>` output of the comparator 143b rises to a high logic level. When the instant measurement data are between the low and high measurement limits, one of the inputs of each OR gate 152a, 152b rises to a high logic level, thereby forcing both inputs of AND gate 155a to rise to a high logic level, which in turn forces the output of the latter to rise to a high logic level. The outputs PASS, FAIL LOW LIMIT, and FAIL HIGH LIMIT may be connected to respective inputs C1, C2, and C3 of the color control 50. By way of an example, display 40 may illuminate in green color for pass, in yellow color for fail on the low limit, and in red color for fail on the high limit.

In FIG. 67 is shown a simplified schematic diagram of the limit memory, limit comparator, and error memory combination, in a digital multimeter for making a series of measurements. A memory 132c contains data symbolizing low measurement limits for each measurement step. A like memory 132d contains data symbolizing high measurement limits for each measurement step. An 8-bit counter 161, which is incremented for each measurement step by a suitable clock pulse, is used to simultaneously address both memories 132c, 132d. When addressed for a particular measurement step, the memories 132c, 132d present the data residing at such address to the inputs B0 to B7 of comparators 143c, 143d, respectively, as the instant low and high measurement limits. The comparison of the instant measurement data with the instant measurement limits is performed by comparators 143c, 143d at each measurement step. When the measurement passes, the PASS output rises to a high logic level. When the measurement fails, either on the low or high measurement limit, the FAIL output of OR gate 152e rises to a high logic level, and error memory 135a is incremented by the next clock pulse. Thus the error memory 135a contains data representing the total number of measurement errors. A logic circuit 150b converts the instant error memory data to color control signals C2 to Cn, whereby the instant measured value is displayed in the color C1 on pass, and in a certain of the colors C2 to Cn on fail, depending on the total number of previous measurement errors, as will be more fully explained later.

In FIG. 68 is shown a detail of the comparator, error flip-flop, and color control combination generally shown in FIG. 65. When a measurement error occurs, either on the low or high measurement limit, the output of an OR gate 152f, which is connected to the D input of error flip-flop 138a, rises to a high logic level, and the error flip-flip will be set by the next clock pulse, to indicate that there was a measurement error. The error flip-flop may be suitably reset (not shown), e. g., at the beginning of each measurement series. Results of the measurements are indicated on display 40 in digital format and in a color depending on the result of comparison with the instant low and high measurement limits and on the condition of the error flip-flop. By way of an example, the measurements may be displayed in green color on pass, in yellow color on fail with no previous measurement errors, and in red color on fail with previous measurement errors.

FIG. 69 is another exemplary detail of the comparator, error memory, and color converter combination generally shown in FIG. 67. When a measurement error occurs, the output of an OR gate 152g, which is connected to the DATA input of the error memory 135b, rises to a high logic level, and the error memory contents will be incremented by the next clock pulse. The error memory 135b thus contains data indicating the total number of previous measurement errors. The outputs of error memory 135b are applied to interconnected inputs of red color converter 59a, green color converter 59b, and blue color converter 59c, which develop drive signals for energizing red bus 5, green bus 6, and blue bus 7 of display 40 to illuminate it in a color related to the total number of previous errors.

FIG. 70 is a detail of the low limit memory and comparator combination shown in FIG. 66. An 8-bit latch 134 stores data representing the instant low measurement limit, which may be from time to time entered via its inputs D0 to D7 (not shown). Two 4-bit digital comparators 142a, 142b are cascaded to form an 8-bit digital comparator, in a manner well understood by those skilled in the art.

FIG. 71 is an exemplary detail of the error counter and PROM combination shown in FIG. 69. An 8-bit counter 163, which contains the count indicating the total number of previous measurement errors, is employed to address, via its outputs Q0 to Q7, a PROM 77 containing the color conversion data which may be used to develop drive signals for red bus 5, green bus 6, and blue bus 7, as previously shown in FIG. 35, to thereby illuminate display 40 in a color depending on the total number of previous measurement errors.

The schematic diagram shown in FIG. 72 includes a digital multimeter 103 for making repeated measurements of input signals and for developing at its outputs a 4-digit BCD code having relation to the magnitude of the instant input signal, and two cascaded registered comparators 145a, 145b for comparing the instant measured value with the value previously stored. From time to time, a short positive pulse 99n may be applied to interconnected Load inputs S0, S1, to cause the instant data at the inputs I0 to I7 of both registered comparators 145a, 145b to be loaded therein. The subsequent measured values will be compared with the reference value currently loaded in the register, and interconnected outputs LT (Less Than), EQ (Equal), GT (Greater Than), which are tied to the supply voltage via suitable pull-up resistors 124f, 124g, 124h, will indicate the result of each comparison. The comparator outputs are respectively connected to the color control inputs C1, C2, C3 of the color control circuit 50, to control the color of display 40, shown in FIG. 62, in accordance with the result of the comparison. The display 40 indicates the instant measured value in digital format and in a color depending on the result of comparison with the reference value currently stored in the register. By way of an example, display 40 may illuminate in green color when the instant measured value is equal to the reference value, in yellow color when it is less than the reference value, and in red color when it is larger than the reference value.

In FIG. 73 is shown a simplified schematic diagram of a digital voltmeter with 31/2 digit variable color display. The digital voltmeter 107 is configured, by having its initialize conversion input INIT connected to a high logic level, to continuously convert input analog voltage, applied to its input terminal via a resistor 124a, to 31/2 digit BCD code corresponding to the magnitude of instant input voltage. The BCD codes for the respective digits are converted, by 7-segment decoders 22a, 22b, 22c, 22d, to signals for directly energizing the segments of the variable color display digits 42a, 42b, 42c, 42d, respectively, in a manner well understood by those skilled in the art. The color control circuit 50 causes all four display digits to illuminate uniformly in a selected color, as previously described.

A like block diagram shown in FIG. 74 differs in that four color control circuits 50a, 50b, 50c, 50d are employed to independently control the colors of respective display digits 42a, 42b, 42c, 42d.

In FIG. 75 is shown, in a block diagram configuration, a multimeter utilizing two digital voltmeters 109a and 109b for measuring respective INPUT SIGNALS 1 and 2. The measured values of both input signals are simultaneously indicated on a single 8-digit variable color display element 42 such that the four most significant display digits D1 to D4 indicate the output of digital voltmeter 109a, and the four least significant display digits D5 to D8 indicate the output of digital voltmeter 109b. In order to clearly distinguish between the two measured values, without the need for a visual gap therebetween, the color control circuit 52a is adapted, by having its color control input G connected to a high logic level, to illuminate the four most significant display digits D1 to D4 in green color, and like color control circuit 52b is adapted, by having its color control input R connected to a high logic level, to illuminate the four least significant digits D5 to D8 in red color.

FIG. 76 is a block diagram of an RMS digital voltmeter with variable color crest factor indication. The RMS (Root Mean Square) value of the measured waveform is its heating value when applied to a resistor; it indicates the magnitude of the measured waveform regardless of its shape. The Crest Factor is the peak signal value divided by the RMS value; it indicates what type of a waveform it is.

The digital voltmeter includes an RMS converter 181 for converting an input measured signal to a DC value representative of the energy content of the measured signal. The DC value from the RMS converter 181 is applied to the HI input terminal of a digital voltmeter 105 which develops at its outputs signals to directly drive variable color digital display 40, to thereby indicate the measured RMS value in digital format, in a manner well known to those having ordinary skill in the art.

The invention resides in the addition of a crest factor converter 183 for computing the crest factor value of the measured waveform, and of a color converter 55 for controlling the color of display 40 in accordance with the crest factor value. The RMS digital voltmeter of the present invention will simultaneously indicate the RMS value of the measured waveform in digital format and in a color indicative of the crest factor value of the measured waveform, to thereby simultaneously indicate its magnitude and shape.

FIG. 77 is a comparison chart of RMS and crest factor values for several exemplary waveforms. It is readily apparent that the crest factor value is a good indication of the waveform shape. The unity value of the crest factor indicates that the measured signal is either a symmetrical waveform or a DC signal. Small values of the crest factor (less than 2) usually indicate either a sine wave, triangle wave, or a low duty cycle pulse train. High values of the crest factor (greater than 4) usually indicate a noise signal or a pulse train with a high duty cycle.

As illustrated in FIG. 78, the crest factor converter 183 includes a ratio producing circuit 187 that develops at its output RATIO A:B a signal representative of the ratio of signals applied to its inputs A and B. The peak signal value, obtained from the output of the peak detector 185, is applied to the input A. The RMS signal value, obtained from the output of the RMS-to-DC converter 181, is applied to the input B. The computed ratio of the peak signal value to the RMS signal value, developed at the output RATIO A:B, is by definition a crest factor value of the measured signal.

In a simplified exemplary schematic diagram of a ratio producing circuit, shown in FIG. 79, the output DC voltage of the RMS-to-DC converter 181 is applied to the X1 input of a precision divider 188, while the output DC voltage of the peak detector 185 is applied to its input Z2. The precision divider 188 develops at its output suitably scaled DC voltage representing the ratio of the signals Z2 to X1.

In an exemplary detail of the RMS converter circuit, shown in FIG. 80, the measured signal is applied, via suitable potentiometer 127c, to the input of an RMS-to-DC converter 182, which develops at its output a DC voltage corresponding to RMS value of the measured signal. The potentiometer 127b and resistors 124p, 124r are used to adjust offset voltage; the capacitor 129p is selected to set a suitable averaging time constant.

FIG. 81 is an exemplary detail of the peak detector circuit, in which a measured signal is applied, via a suitable resistor 124u, to the input of a peak detector 186, which develops at its output a DC voltage, retained on the hold capacitor 129r, representing the maximum value of the input signal. The present peak value may be from time to time reset, by applying a relatively short positive pulse 99p to interconnected inputs DET and RESET. When pulse 99p returns to a low logic level, new peak of the input signal may be measured.

As shown in FIG. 82 in a block diagram form, the output voltage of the crest factor converter, which indicates the instant measured value of the crest factor, may be applied to input of a suitable comparator 141a, such as the one shown in FIG. 23, to develop color control logic signals R, Y, G for the color control circuit 52, to illuminate display element 42 in one of three colors, in accordance with the value of the crest factor. By way of an example, the comparator 141a may be set to develop active color control signal G for values of the crest factor less than 1.5, to illuminate display element 42 in green color, active color control signal Y for values of the crest factor between 1.5 and 2.5, to illuminate display element 42 in yellow color, and active color control signal R for values of the crest factor greater than 2.5, to illuminate display element 42 in red color.

A similar block diagram shown in FIG. 83 differs in that a comparator 141b, such as the one shown in FIG. 25, and color control circuit 53 are used to illuminate display element 43 in one of seven colors, in accordance with the value of the crest factor. By way of an example, the comparator 141b may develop active color control signal B for values of the crest factor less than 1.1, to illuminate display element 43 in blue color, active color control signal P for values of the crest factor between 1.1 and 1.4, to illuminate display element 43 in purple color, active color control signal BG for crest factor values between 1.4 and 1.7, to illuminate display element 43 in blue-green color, active color control signal G for crest factor values between 1.7 and 2.0, to illuminate display element 43 in green color, active color control signal Y for crest factor values between 2.0 and 2.5, to illuminate display element 43 in yellow color, active color control signal W for crest factor values between 2.5 and 3.0, to illuminate display element 43 in white color, active color control signal R for crest factor values greater than 3.0, to illuminate display element 43 in red color.

As shown in FIG. 84, the output voltage of the crest factor converter 183 is applied to the input of a scaling circuit 80a, such as the one shown in FIG. 31, to be scaled and shifted to a voltage range suitable for the continuous 2-primary color converter 57, which will develop drive signals for controlling red bus 5 and green bus 6, respectively, of display 42, to illuminate it in a color related to the instant measured value of the crest factor.

A like block diagram shown in FIG. 85 differs in that 3-primary color converter 58 is used to develop drive signals for red bus 5, green bus 6, and blue bus 7, respectively, of display element 43, to illuminate it in a color related to the measured value of the crest factor. The relationship between the crest factor values and the color of display element 43 may be defined at will, e. g., by programming suitable data into PROMs contained in color converter 58, as previously described.

In FIG. 86 is shown a front view of a digital multimeter which includes a 61/2 digit variable color digital display 49, keyboard 117, and suitable terminals 116 for attaching thereto the measuring cords. The keyboard 117 includes a DC V key 118a for setting the multimeter to its DC voltage mode, AC V key 118b for setting the multimeter to its AC voltage mode, OHMS key 118c for setting the multimeter to its OHMS mode, RANGE keys 118d, 118e, 118f, 118g, 118h, 118i for setting the multimeter to a selected range, LOCAL key 118j for setting the multimeter to its local mode, FRONT key 118k for selecting front measurement terminals, FILTER key 118m for setting the multimeter to its filter mode, AUTO key 118n for setting the multimeter to its autoranging mode, OFFS key 118p, `%` key 118r, and LAH key 118s for setting the multimeter to certain of its mathematical modes. The HI INPUT terminal 116a and LO INPUT terminal 116b may be used for voltage measurements; the like HI OHM terminal 116c and LO OHM terminal 116d may be used for resistance measurements.

In FIG. 87 is shown a block diagram of a variable color digital multimeter controlled by a microprocessor or microcomputer 168, which can be influenced either locally, by entering commands via the keyboard 117, or remotely, by sending commands over a bus via the remote control circuit 169. When properly commanded, the microprocessor 168 can control the input conditioning section 120, AC section 112, and OHMS section 113, to selectively switch, scale, attenuate, rectify, and filter the measured signals, before being applied to the input of an A/D converter 106, which repeatedly performs analog-to-digital conversions and develops output data indicative of the magnitude of the instant measured signal. The microprocessor 168 can from time to time read output data of the converter 106 and send same to display controller 167, which causes the data to be indicated on display 40 in digital format. The invention resides in the addition of a color memory 136, wherein data symbolizing a selected color may be stored, and color control 50 for illuminating display 40 in the selected color. It is contemplated that the color of display 40 may be controlled in accordance with certain of the following operating modes:

a. Local/remote mode: The multimeter may be set either to its local mode, e. g., by actuating the LOCAL key 118j on the front panel, wherein all commands are entered via the keyboard 117, and the remote control 169 is disabled, or to its remote mode wherein all commands are sent via the remote control 169, and the keyboard 117 is disabled. When in its local mode, microprocessor 168 will send data to the color memory 136 commanding color control 50 to illuminate display 40 in a first color (e. g., green); when in its remote mode, microprocessor 168 will send different data to color memory 136 commanding that display 40 be illuminated in a second color (e. g., red), so that an operator may readily distinguish the two modes.

b. Normal/offset mode: The multimeter may be set to its offset mode, e. g., by actuating the OFFS key 118p on the front panel, wherein a numeric constant (an offset) is stored in the microprocessor's memory, to calculate and display the difference between a measured value and the offset; when in its normal mode, the multimeter displays true measured values. To indicate in which mode the multimeter currently operates, the microprocessor 168 will send data to the color memory 136 commanding that display 40 be illuminated in a first color when in its normal mode and in a second color when in its offset mode.

c. Standard/percent mode: The multimeter may be set to its percent mode, e. g., by actuating the `%` key 118r on the front panel, wherein a percent deviation of a measured value from a value stored in the microprocessor's memory (reference value) is calculated and displayed; when in its standard mode, true measured values are displayed. To indicate in which mode the multimeter currently operates, microprocessor 168 will send data to color memory 136 commanding that display 40 be illuminated in a first color for the standard mode and in a second color for the percent mode.

d. LAH/standard mode: The multimeter may be set to its LAH (Low, Average, High) mode, e. g., by actuating the LAH key 118s on the front panel, wherein the multimeter will store the most positive and most negative measured values, calculate the average measured value, and count the number of measurements during the LAH cycle; when in its standard mode, true measured values are displayed. To indicate whether the multimeter currently operates in the standard or LAH mode, the microprocessor 168 will send data to the color memory 136 commanding that display 40 be illuminated in a first color for the standard mode and in a second color for the LAH mode.

In FIG. 88 is shown an expanded block diagram of a digital multimeter with a DC section 111 for processing DC signals, AC section 112 for processing AC signals, and OHMS section 113 for performing resistance measurements, as will be more fully explained later. The multimeter includes input terminals HI INPUT 116a, LO INPUT 116b, HI OHM 116c, LO OHM 116d on the front panel shown in FIG. 86, and like input terminals on the rear panel (not shown), which may be selectively connected to the input of a digital voltmeter 105. To select between the front and rear measurements, the FRONT key 118k may be actuated, which toggles a front/rear relay 191 between its energized and disenergized conditions.

To facilitate the illustration, a convention was adopted that a particular relay is designated in the drawings by a certain numeral, and its associated contacts are designated by same numeral with character `a`, `b`, etc., appended. By way of an example, relay 191 has contacts 191a, 191b, 191c, 191d, 191e. When relay 191 is not energized, its contacts 191a to 191e are in the positions as illustrated, thereby making available the front input terminals for connection to the input of digital voltmeter 105. When relay 191 is energized, its contacts 191a to 191e switch to their other positions, respectively, thereby making available the rear input terminals for connection to the input of the digital voltmeter 105. The invention resides in the addition of relay contact 191e, associated with contacts 191a to 191d, such that the front and rear measurements are indicated in a digital format and in respectively different colors. When the measurements via the front input terminals are performed, as illustrated, relay contact 191e is open, and the color control input C1 is pulled to a low logic level by a suitable pull-down resistor 124v, thereby forcing, via an inverter 151e, the color control input C2 to rise to a high logic level, to thereby cause display 40 to be illuminated in the color C2 (e. g., red). When the measurements via the rear input terminals are performed, by causing relay 191 to be energized to switch its contacts 191a to 191e to their other positions, respectively, contact 191e is closed to apply a high logic level from the source +VCC to the color control input C1, and to simultaneously force, via inverter 151e, the color control input C2 to a low logic level, to thereby cause display 40 to be illuminated in the color C1 (e. g., green).

In FIG. 89 is shown a like block diagram of a digital multimeter for selectively performing DC, AC, and OHMS measurements and for indicating measured values in digital format and in respectively different colors. To perform DC measurements, the DC relay 192 is energized, e. g., by actuating the DC V key 118a on the front panel of the, to connect the HI INPUT terminal, via contact 191a and closed contact 192a, and via the DC section 111, to the HI input of digital voltmeter 105. Simultaneously, the LO relay 195 is energized to connect the LO INPUT terminal, via contact 191b and closed contact 195a, to the LO input of digital voltmeter 105. Measured DC values of the input signal are indicated on display 40 in digital format, in a manner well understood by those skilled in the art. The invention resides in the provision of a relay contact 192b, associated with contact 192a, to apply a high logic level to the color control input C1, to cause display 40 to illuminate in the color C1 (e. g., red).

To perform AC measurements, the AC relay 193 is energized, e. g., by actuating the AC V key 118b on the multimeter's front panel, to connect the HI INPUT terminal, via contact 191a and closed contact 193a, and via the AC section 112, to the HI input of digital voltmeter 105. Simultaneously, LO relay 195 is energized to connect the LO INPUT terminal to the LO input of the digital voltmeter 105. Measured AC values of the input signal are indicated on display 40 in digital format, in a manner well understood. The relay contact 193b, associated with contact 193a, closes when relay 193 is energized, to apply a high logic level to the color control input C2, to cause display 40 to illuminate in the color C2 (e. g., yellow).

To perform OHMS measurements, the OHMS relay 124 is energized, e. g., by actuating the OHMS key 118c on the multimeter's front panel, to connect the HI OHM terminal, via closed contact 194a, and via OHMS section 113, to the HI input of digital voltmeter 105. The LO OHM terminal is connected, via closed contact 194b, to the LO input of digital voltmeter 105. Measured resistance values are indicated on display 40 in digital format, in a manner well known. The relay contact 194c, associated with contacts 194a, 194b, closes when relay 194 is energized, to apply a high logic level to the color control input C3, to cause display 40 to illuminate in the color C3 (e. g., green).

The digital voltmeter shown in FIG. 90 may be set to its filter mode wherein the measured signal is filtered to remove high frequency noise. The invention resides in the addition of a filter flip-flop 138b for activating color control circuit 50 to illuminate display 40 in the color C1 for the filter mode turned on and in the color C2 for the filter mode turned off. The filter mode may be turned on and off by actuating the FILTER key 118m, to toggle filter flip-flop 138b. When key 118m is actuated, its associated keyswitch 119m momentarily closes, to connect a low logic level to the trigger input TRG of a timer 158, which is normally tied to a high logic level via its pull-up resistor 124i, to produce at the timer's output OUT a relatively short positive going pulse 99s, to trigger filter flip-flop 138b to its opposite state. The width of pulse 99s may be set by selecting suitable values of resistor 124z and capacitor 129s, to eliminate the problem of possible bouncing of keyswitch 119m. When flip-flop 138b is in its set condition, its output Q, which is connected to the input of a relay driver 157, rises to a high logic level, to activate the latter, to energize filter relay 196. The associated relay contact 196a closes to connect filter circuit 149 to the input of digital voltmeter 105. The outputs Q and Q of flip-flop 138b are connected to the color control inputs C1, C2, respectively, to cause display 40 to illuminate in a color in accordance with the condition of flip-flop 138b.

In brief summary, the invention describes a variable color digital measuring instrument which comprises a plurality of adjacent variable color light emitting diode digital display elements for sequentially providing a digital indication of a first measured value of a signal and of a second measured value of the signal, in accordance with a first timing signal and a second timing signal, respectively, developed by a timing device. A memory is provided for storing the data corresponding to the first measured value, in accordance with the first timing signal. A comparator is also provided for comparing the second measured value, in accordance with the second timing signal, with the data stored in the memory and for developing a first comparison signal when the second measured value is larger than the data stored in the memory and a second comparison signal when the second measured value is less than the data stored in the memory. A color control is also provided for uniformly controlling the color of the digital indication, in accordance with the second timing signal, for illuminating the digital indication in a first color in response to the first comparison signal and in a second color in response to the second comparison signal.

It would be obvious, in the view of the present disclosure, that the hardware design of the present invention may be also implemented by software. It would be further obvious that persons skilled in the art may resort to modifications in the construction of the preferred embodiment described herein, without departing from the spirit and scope of the invention as defined in the appended claims. It is contemplated that the principles of the invention are also applicable to numerous diverse types of display devices, such as luminescent devices, liquid crystal display devices, plasma display devices, cathode ray tube display devices, and the like.

    ______________________________________                                         CORRELATION TABLE                                                              This is a correlation table of reference characters used in                    the drawings herein, their descriptions, and examples of                       commercially available parts.                                                  #    DESCRIPTION               EXAMPLE                                         ______________________________________                                         1    display segment                                                           2    red LED                                                                   3    green LED                                                                 4    blue LED                                                                  5    red bus                                                                   6    green bus                                                                 7    blue bus                                                                  10   device developing electric signals                                        11   analog voltage source                                                     12   digital device                                                            15   segment body                                                              16   light scattering material                                                 20   decoder                                                                   21   digital decoder driver                                                    22   7-segment display decoder driver                                          23   common cathode 7-segment decoder driver                                                                  74LS49                                          24   common anode 7-segment decoder driver                                                                    74LS47                                          30   monochromatic digital display                                             40   variable color digital display                                            41   multiplexed variable color display                                        42   variable color 7-segment display element (2 LEDs)                         43   variable color 7-segment display element (3 LEDs)                         46   variable color display element (2 LEDs)                                   47   variable color display element (3 LEDs)                                   48   31/2 digit variable color display                                         49   61/2 digit variable color 7-segment display                               50   color control                                                             51   step variable color control                                               52   color control (2 LEDs)                                                    53   color control (3 LEDs)                                                    55   color converter                                                           56   continuously variable color converter                                     57   2-primary color converter                                                 58   3-primary color converter                                                 59   single color converter                                                    60   2-input OR gate           74HC32                                          61   4-input OR gate           4072                                            62   non-inverting buffer      74LS244                                         63   inverting buffer          74LS240                                         64   inverter                  part of                                                                        74LS240,4                                       65   inverter                  74HC04                                          66   2-input AND gate          74HC08                                          67   priority encoder          74HC147                                         68   3-to-8 line decoder       74HC138                                         69   logic circuit                                                             71   8-bit counter             74F579                                          73   D type flip-flop          74HC74                                          74   A/D converter                                                             75   8-bit A/D converter       AD570                                           76   memory                                                                    77   2k × 8 bit PROM     2716                                            80   scaling circuit                                                           81   op amp                    LM741                                           82   analog comparator         LM339                                           85   signal converter                                                          90   resistor                                                                  91   resistor                                                                  92   potentiometer                                                             93   capacitor                                                                 99   pulse                                                                     101  multimeter                                                                102  multimeter with multiplexed outputs                                       103  digital multimeter                                                        105  digital voltmeter                                                         106  A/D converter                                                             107  Teledyne DVM chip         TSC8750                                         108  Teledyne DVM chip         TSC7107                                         109  Intersil DVM chip         ILS7107                                         111  DC section                                                                112  AC section                                                                113  OHMS section                                                              115  control section                                                           116  measuring terminal                                                        117  keyboard                                                                  118  key                                                                       119  keyswitch                                                                 120  input conditioning                                                        121  selector                                                                  123  rotary switch                                                             124  resistor                                                                  125  resistor                                                                  126  precision resistor                                                        127  potentiometer                                                             128  signal diode              1N4148                                          129  capacitor                                                                 131  memory                                                                    132  8-bit wide memory                                                         134  8-bit latch               74HC273                                         135  error memory                                                              136  color memory                                                              138  D-type flip-flop          74HC74                                          141  comparator                                                                142  4-bit digital comparator  74HC85                                          143  8-bit digital comparator                                                  144  memory & comparator                                                       145  registered comparator     74F524                                          146  8-channel digital multiplexer                                                                            74HC151                                         147  analog multiplexer        4051                                            148  clock                                                                     149  filter                                                                    150  logic circuit                                                             151  inverter                  74HC04                                          152  2-input OR gate           74HC32                                          154  8-input OR/NOR gate       74HC4078                                        155  2-input AND gate          74HC08                                          156  3-input AND gate          74HC11                                          157  relay driver              1416                                            158  timer                     NE555                                           159  op amp                    LM741                                           161  counter                                                                   162  4-bit binary counter      74HC161                                         163  8-bit binary counter      74F579                                          164  3-decade counter          14553                                           165  decoder                                                                   166  1-to-8 lines decoder      74HC138                                         167  display controller        ICM7218A                                        168  microprocessor            8085                                            169  remote control                                                            172  temperature transducer                                                    173  pressure transducer                                                       174  physiological transducer                                                  176  SenSym pressure transducer                                                                               LX1802AN                                        177  Kelvin temperature transducer                                             178  Celsius temperature transducer                                                                           LM35                                            179  Fahrenheit temperature transducer                                                                        LM34                                            181  RMS to DC converter                                                       182  RMS converter chip        AD536A                                          183  crest factor converter                                                    185  peak detector                                                             186  peak detector chip        PKD-01                                          187  ratio producing circuit                                                   188  precision divider chip    AD535                                           191  front/rear relay          JDT21                                           192  DC section relay          JDT7                                            193  AC section relay          JDT7                                            194  OHMS section relay        JDT15                                           195  LO input relay            JWD-107                                         196  filter relay              JWD-107                                         199  pulse                                                                     ______________________________________                                    

The examples of commercially available components should be considered as merely illustrative. It will be appreciated that other components may be readily and effectively used. The integrated circuits used in the description of the invention are manufactured by several well known companies, such are Analog Devices, Inc., Fairchild Camera and Instrument Corporation, Intel Corporation, Intersil, Inc., Motorola Semiconductor Products Inc., National Semiconductor Incorporated, Precision Monolithics Incorporated, Teledyne Semiconductor, Texas Instruments Inc., etc.

                  TABLE 1                                                          ______________________________________                                                  DATA PORTIONS                                                         Input      PROM    `Red`                                                       Voltage    Address PROM                                                        (Volts)    (Hex)   (Hex)       red  green                                      ______________________________________                                         0.0        00      00          0.0  1.0                                        0.039      01      00          0.0  1.0                                        0.078      02      00          0.0  1.0                                        0.117      03      00          0.0  1.0                                        0.156      04      00          0.0  1.0                                        0.195      05      00          0.0  1.0                                        0.234      06      00          0.0  1.0                                        0.273      07      00          0.0  1.0                                        0.312      08      00          0.0  1.0                                        0.352      09      00          0.0  1.0                                        0.391      0A      00          0.0  1.0                                        0.430      0B      00          0.0  1.0                                        0.469      0C      00          0.0  1.0                                        0.508      0D      00          0.0  1.0                                        0.547      0E      00          0.0  1.0                                        0.586      0F      00          0.0  1.0                                        0.625      10      40          0.25 0.75                                       0.664      11      40          0.25 0.75                                       0.703      12      40          0.25 0.75                                       0.742      13      40          0.25 0.75                                       0.781      14      40          0.25 0.75                                       0.820      15      40          0.25 0.75                                       0.859      16      40          0.25 0.75                                       0.898      17      40          0.25 0.75                                       0.937      18      40          0.25 0.75                                       0.977      19      40          0.25 0.75                                       1.016      1A      40          0.25 0.75                                       1.055      1B      40          0.25 0.75                                       1.094      1C      40          0.25 0.75                                       1.133      1D      40          0.25 0.75                                       1.172      1E      40          0.25 0.75                                       1.211      1F      40          0.25 0.75                                       1.250      20      80          0.5  0.5                                        1.289      21      80          0.5  0.5                                        1.328      22      80          0.5  0.5                                        1.367      23      80          0.5  0.5                                        1.406      24      80          0.5  0.5                                        1.445      25      80          0.5  0.5                                        1.484      26      80          0.5  0.5                                        1.523      27      80          0.5  0.5                                        1.562      28      80          0.5  0.5                                        1.602      29      80          0.5  0.5                                        1.641      2A      80          0.5  0.5                                        1.680      2B      80          0.5  0.5                                        1.719      2C      80          0.5  0.5                                        1.758      2D      80          0.5  0.5                                        1.797      2E      80          0.5  0.5                                        1.836      2F      80          0.5  0.5                                        1.875      30      C0          0.75 0.25                                       1.914      31      C0          0.75 0.25                                       1.953      32      C0          0.75 0.25                                       1.992      33      C0          0.75 0.25                                       2.031      34      C0          0.75 0.25                                       2.070      35      C0          0.75 0.25                                       2.109      36      C0          0.75 0.25                                       2.148      37      C0          0.75 0.25                                       2.187      38      C0          0.75 0.25                                       2.227      39      C0          0.75 0.25                                       2.266      3A      C0          0.75 0.25                                       2.305      3B      C0          0.75 0.25                                       2.344      3C      C0          0.75 0.25                                       2.389      3D      C0          0.75 0.25                                       2.422      3E      C0          0.75 0.25                                       2.461      3F      C0          0.75 0.25                                       2.500      40      FF          1.0  0.0                                        2.539      41      FF          1.0  0.0                                        2.578      42      FF          1.0  0.0                                        2.617      43      FF          1.0  0.0                                        2.656      44      FF          1.0  0.0                                        2.695      45      FF          1.0  0.0                                        2.734      46      FF          1.0  0.0                                        2.773      47      FF          1.0  0.0                                        2.812      48      FF          1.0  0.0                                        2.852      49      FF          1.0  0.0                                        2.891      4A      FF          1.0  0.0                                        2.930      4B      FF          1.0  0.0                                        2.969      4C      FF          1.0  0.0                                        3.008      4D      FF          1.0  0.0                                        3.047      4E      FF          1.0  0.0                                        3.086      4F      FF          1.0  0.0                                        3.125      50      00          0.0  1.0                                        3.164      51      00          0.0  1.0                                        3.203      52      00          0.0  1.0                                        3.242      53      00          0.0  1.0                                        3.281      54      00          0.0  1.0                                        3.320      55      00          0.0  1.0                                        3.359      56      00          0.0  1.0                                        3.398      57      00          0.0  1.0                                        3.437      58      00          0.0  1.0                                        3.477      59      00          0.0  1.0                                        3.516      5A      00          0.0  1.0                                        3.555      5B      00          0.0  1.0                                        3.594      5C      00          0.0  1.0                                        3.633      5D      00          0.0  1.0                                        3.672      5E      00          0.0  1.0                                        3.711      5F      00          0.0  1.0                                        3.750      60      40          0.25 0.75                                       3.789      61      40          0.25 0.75                                       3.828      62      40          0.25 0.75                                       3.867      63      40          0.25 0.75                                       3.906      64      40          0.25 0.75                                       3.945      65      40          0.25 0.75                                       3.984      66      40          0.25 0.75                                       4.023      67      40          0.25 0.75                                       4.062      68      40          0.25 0.75                                       4.102      69      40          0.25 0.75                                       4.141      6A      40          0.25 0.75                                       4.178      6B      40          0.25 0.75                                       4.219      6C      40          0.25 0.75                                       4.258      6D      40          0.25 0.75                                       4.299      6E      40          0.25 0.75                                       4.336      6F      40          0.25 0.75                                       4.375      70      80          0.5  0.5                                        4.414      71      80          0.5  0.5                                        4.453      72      80          0.5  0.5                                        4.492      73      80          0.5  0.5                                        4.531      74      80          0.5  0.5                                        4.570      75      80          0.5  0.5                                        4.609      76      80          0.5  0.5                                        4.648      77      80          0.5  0.5                                        4.687      78      80          0.5  0.5                                        4.727      79      80          0.5  0.5                                        4.766      7A      80          0.5  0.5                                        4.805      7B      80          0.5  0.5                                        4.844      7C      80          0.5  0.5                                        4.883      7D      80          0.5  0.5                                        4.922      7E      80          0.5  0.5                                        4.961      7F      80          0.5  0.5                                        5.000      80      C0          0.75 0.25                                       5.039      81      C0          0.75 0.25                                       5.078      82      C0          0.75 0.25                                       5.117      83      C0          0.75 0.25                                       5.156      84      C0          0.75 0.25                                       5.195      85      C0          0.75 0.25                                       5.234      86      C0          0.75 0.25                                       5.273      87      C0          0.75 0.25                                       5.312      88      C0          0.75 0.25                                       5.352      89      C0          0.75 0.25                                       5.391      8A      C0          0.75 0.25                                       5.430      8B      C0          0.75 0.25                                       5.469      8C      C0          0.75 0.25                                       5.508      8D      C0          0.75 0.25                                       5.547      8E      C0          0.75 0.25                                       5.586      8F      C0          0.75 0.25                                       5.625      90      FF          1.0  0.0                                        5.664      91      FF          1.0  0.0                                        5.703      92      FF          1.0  0.0                                        5.742      93      FF          1.0  0.0                                        5.781      94      FF          1.0  0.0                                        5.820      95      FF          1.0  0.0                                        5.859      96      FF          1.0  0.0                                        5.898      97      FF          1.0  0.0                                        5.937      98      FF          1.0  0.0                                        5.977      99      FF          1.0  0.0                                        6.016      9A      FF          1.0  0.0                                        6.055      9B      FF          1.0  0.0                                        6.094      9C      FF          1.0  0.0                                        6.133      9D      FF          1.0  0.0                                        6.172      9E      FF          1.0  0.0                                        6.211      9F      FF          1.0  0.0                                        6.250      A0      00          0.0  1.0                                        6.289      A1      00          0.0  1.0                                        6.328      A2      00          0.0  1.0                                        6.367      A3      00          0.0  1.0                                        6.406      A4      00          0.0  1.0                                        6.445      A5      00          0.0  1.0                                        6.484      A6      00          0.0  1.0                                        6.524      A7      00          0.0  1.0                                        6.562      A8      00          0.0  1.0                                        6.602      A9      00          0.0  1.0                                        6.641      AA      00          0.0  1.0                                        6.680      AB      00          0.0  1.0                                        6.719      AC      00          0.0  1.0                                        6.758      AD      00          0.0  1.0                                        6.797      AE      00          0.0  1.0                                        6.836      AF      00          0.0  1.0                                        6.875      B0      40          0.25 0.75                                       6.914      B1      40          0.25 0.75                                       6.953      B2      40          0.25 0.75                                       6.992      B3      40          0.25 0.75                                       7.031      B4      40          0.25 0.75                                       7.070      B5      40          0.25 0.75                                       7.109      B6      40          0.25 0.75                                       7.148      B7      40          0.25 0.75                                       7.187      B8      40          0.25 0.75                                       7.227      B9      40          0.25 0.75                                       7.266      BA      40          0.25 0.75                                       7.305      BB      40          0.25 0.75                                       7.344      BC      40          0.25 0.75                                       7.383      BD      40          0.25 0.75                                       7.422      BE      40          0.25 0.75                                       7.461      BF      40          0.25 0.75                                       7.500      C0      80          0.5  0.5                                        7.539      C1      80          0.5  0.5                                        7.587      C2      80          0.5  0.5                                        7.617      C3      80          0.5  0.5                                        7.656      C4      80          0.5  0.5                                        7.695      C5      80          0.5  0.5                                        7.734      C6      80          0.5  0.5                                        7.773      C7      80          0.5  0.5                                        7.812      C8      80          0.5  0.5                                        7.852      C9      80          0.5  0.5                                        7.891      CA      80          0.5  0.5                                        7.930      CB      80          0.5  0.5                                        7.969      CC      80          0.5  0.5                                        8.008      CD      80          0.5  0.5                                        8.047      CE      80          0.5  0.5                                        8.086      CF      80          0.5  0.5                                        8.125      D0      C0          0.75 0.25                                       8.164      D1      C0          0.75 0.25                                       8.203      D2      C0          0.75 0.25                                       8.242      D3      C0          0.75 0.25                                       8.281      D4      C0          0.75 0.25                                       8.320      D5      C0          0.75 0.25                                       8.359      D6      C0          0.75 0.25                                       8.398      D7      C0          0.75 0.25                                       8.437      D8      C0          0.75 0.25                                       8.477      D9      C0          0.75 0.25                                       8.516      DA      C0          0.75 0.25                                       8.555      DB      C0          0.75 0.25                                       8.594      DC      C0          0.75 0.25                                       8.633      DD      C0          0.75 0.25                                       8.672      DE      C0          0.75 0.25                                       8.711      DF      C0          0.75 0.25                                       8.750      E0      FF          1.0  0.0                                        8.789      E1      FF          1.0  0.0                                        8.828      E2      FF          1.0  0.0                                        8.867      E3      FF          1.0  0.0                                        8.906      E4      FF          1.0  0.0                                        8.945      E5      FF          1.0  0.0                                        8.984      E6      FF          1.0  0.0                                        9.023      E7      FF          1.0  0.0                                        9.062      E8      FF          1.0  0.0                                        9.102      E9      FF          1.0  0.0                                        9.141      EA      FF          1.0  0.0                                        9.180      EB      FF          1.0  0.0                                        9.219      EC      FF          1.0  0.0                                        9.258      ED      FF          1.0  0.0                                        9.299      EE      FF          1.0  0.0                                        9.336      EF      FF          1.0  0.0                                        9.375      F0      00          0.0  1.0                                        9.414      F1      00          0.0  1.0                                        9.453      F2      00          0.0  1.0                                        9.492      F3      00          0.0  1.0                                        9.531      F4      00          0.0  1.0                                        9.570      F5      00          0.0  1.0                                        9.609      F6      00          0.0  1.0                                        9.648      F7      00          0.0  1.0                                        9.687      F8      00          0.0  1.0                                        9.727      F9      00          0.0  1.0                                        9.766      FA      00          0.0  1.0                                        9.805      FB      00          0.0  1.0                                        9.844      FC      00          0.0  1.0                                        9.883      FD      00          0.0  1.0                                        9.922      FE      00          0.0  1.0                                        9.961      FF      00          0.0  1.0                                        ______________________________________                                    

                  TABLE 2                                                          ______________________________________                                         DATA PORTIONS                                                                  Input PROM    `Red`   `Green`                                                                              `Blue`                                             Voltage                                                                              Address PROM    PROM  PROM                                               (Volts)                                                                              (Hex)   (Hex)   (Hex) (Hex)  red  green                                                                               blue                              ______________________________________                                         0.0   00      FF      00    00     1.0  0.0  0.0                               0.039 01      FE      02    00     0.992                                                                               0.008                                                                               0.0                               0.078 02      FC      04    00     0.984                                                                               0.016                                                                               0.0                               0.117 03      FA      06    00     0.976                                                                               0.024                                                                               0.0                               0.156 04      F8      08    00     0.969                                                                               0.031                                                                               0.0                               0.195 05      F6      0A    00     0.961                                                                               0.039                                                                               0.0                               0.234 06      F4      0C    00     0.953                                                                               0.047                                                                               0.0                               0.273 07      F2      0E    00     0.945                                                                               0.055                                                                               0.0                               0.312 08      F0      10    00     0.937                                                                               0.063                                                                               0.0                               0.352 09      EE      12    00     0.930                                                                               0.070                                                                               0.0                               0.391 0A      EC      14    00     0.922                                                                               0.078                                                                               0.0                               0.430 0B      EA      16    00     0.914                                                                               0.086                                                                               0.0                               0.469 0C      E8      18    00     0.906                                                                               0.094                                                                               0.0                               0.508 0D      E6      1A    00     0.899                                                                               0.101                                                                               0.0                               0.547 0E      E4      1C    00     0.891                                                                               0.109                                                                               0.0                               0.586 0F      E2      1E    00     0.883                                                                               0.117                                                                               0.0                               0.625 10      E0      20    00     0.875                                                                               0.125                                                                               0.0                               0.664 11      DE      22    00     0.867                                                                               0.133                                                                               0.0                               0.703 12      DC      24    00     0.859                                                                               0.141                                                                               0.0                               0.742 13      DA      26    00     0.851                                                                               0.149                                                                               0.0                               0.781 14      D8      28    00     0.844                                                                               0.156                                                                               0.0                               0.820 15      D6      2A    00     0.836                                                                               0.164                                                                               0.0                               0.859 16      D4      2C    00     0.828                                                                               0.172                                                                               0.0                               0.898 17      D2      2E    00     0.820                                                                               0.180                                                                               0.0                               0.937 18      D0      30    00     0.812                                                                               0.188                                                                               0.0                               0.977 19      CE      32    00     0.804                                                                               0.196                                                                               0.0                               1.016 1A      CC      34    00     0.796                                                                               0.204                                                                               0.0                               1.055 1B      CA      36    00     0.788                                                                               0.212                                                                               0.0                               1.094 1C      C8      38    00     0.781                                                                               0.219                                                                               0.0                               1.133 1D      C6      3A    00     0.773                                                                               0.227                                                                               0.0                               1.172 1E      C4      3C    00     0.766                                                                               0.234                                                                               0.0                               1.211 1F      C2      3E    00     0.758                                                                               0.242                                                                               0.0                               1.250 20      C0      40    00     0.75 0.25 0.0                               1.289 21      BE      42    00     0.742                                                                               0.258                                                                               0.0                               1.328 22      BC      44    00     0.734                                                                               0.266                                                                               0.0                               1.367 23      BA      46    00     0.726                                                                               0.274                                                                               0.0                               1.406 24      B8      48    00     0.719                                                                               0.281                                                                               0.0                               1.445 25      B6      4A    00     0.711                                                                               0.289                                                                               0.0                               1.484 26      B4      4C    00     0.703                                                                               0.297                                                                               0.0                               1.523 27      B2      4E    00     0.695                                                                               0.305                                                                               0.0                               1.562 28      B0      50    00     0.687                                                                               0.313                                                                               0.0                               1.602 29      AE      52    00     0.680                                                                               0.320                                                                               0.0                               1.641 2A      AC      54    00     0.672                                                                               0.328                                                                               0.0                               1.680 2B      AA      56    00     0.664                                                                               0.336                                                                               0.0                               1.719 2C      A8      58    00     0.656                                                                               0.344                                                                               0.0                               1.758 2D      A6      5A    00     0.648                                                                               0.352                                                                               0.0                               1.797 2E      A4      5C    00     0.641                                                                               0.359                                                                               0.0                               1.836 2F      A2      5E    00     0.633                                                                               0.367                                                                               0.0                               1.875 30      A0      60    00     0.625                                                                               0.375                                                                               0.0                               1.914 31      9E      62    00     0.613                                                                               0.383                                                                               0.0                               1.953 32      9C      64    00     0.609                                                                               0.391                                                                               0.0                               1.992 33      9A      66    00     0.602                                                                               0.398                                                                               0.0                               2.031 34      98      68    00     0.594                                                                               0.406                                                                               0.0                               2.070 35      96      6A    00     0.586                                                                               0.414                                                                               0.0                               2.109 36      94      6C    00     0.578                                                                               0.422                                                                               0.0                               2.148 37      92      6E    00     0.570                                                                               0.430                                                                               0.0                               2.187 38      90      70    00     0.562                                                                               0.438                                                                               0.0                               2.227 39      8E      72    00     0.554                                                                               0.446                                                                               0.0                               2.266 3A      8C      74    00     0.547                                                                               0.453                                                                               0.0                               2.305 3B      8A      76    00     0.539                                                                               0.461                                                                               0.0                               2.344 3C      88      78    00     0.531                                                                               0.469                                                                               0.0                               2.389 3D      86      7A    00     0.524                                                                               0.476                                                                               0.0                               2.422 3E      84      7C    00     0.516                                                                               0.484                                                                               0.0                               2.461 3F      82      7E    00     0.508                                                                               0.492                                                                               0.0                               2.500 40      80      80    00     0.5  0.5  0.0                               2.539 41      7C      84    00     0.484                                                                               0.516                                                                               0.0                               2.578 42      78      88    00     0.469                                                                               0.531                                                                               0.0                               2.617 43      74      8C    00     0.453                                                                               0.547                                                                               0.0                               2.656 44      70      90    00     0.437                                                                               0.563                                                                               0.0                               2.695 45      6C      94    00     0.422                                                                               0.578                                                                               0.0                               2.734 46      68      98    00     0.406                                                                               0.594                                                                               0.0                               2.773 47      64      9C    00     0.391                                                                               0.609                                                                               0.0                               2.812 48      60      A0    00     0.375                                                                               0.625                                                                               0.0                               2.852 49      5C      A4    00     0.359                                                                               0.641                                                                               0.0                               2.891 4A      58      A8    00     0.344                                                                               0.656                                                                               0.0                               2.930 4B      54      AC    00     0.328                                                                               0.672                                                                               0.0                               2.969 4C      50      B0    00     0.312                                                                               0.688                                                                               0.0                               3.008 4D      4C      B4    00     0.297                                                                               0.703                                                                               0.0                               3.047 4E      48      B8    00     0.281                                                                               0.719                                                                               0.0                               3.086 4F      44      BC    00     0.266                                                                               0.734                                                                               0.0                               3.125 50      40      C0    00     0.25 0.75 0.0                               3.164 51      3C      C4    00     0.234                                                                               0.766                                                                               0.0                               3.203 52      38      C8    00     0.219                                                                               0.781                                                                               0.0                               3.242 53      34      CC    00     0.203                                                                               0.797                                                                               0.0                               3.281 54      30      D0    00     0.187                                                                               0.813                                                                               0.0                               3.320 55      2C      D4    00     0.172                                                                               0.828                                                                               0.0                               3.359 56      28      D8    00     0.156                                                                               0.844                                                                               0.0                               3.398 57      24      DC    00     0.141                                                                               0.859                                                                               0.0                               3.437 58      20      E0    00     0.125                                                                               0.875                                                                               0.0                               3.477 59      1C      E4    00     0.109                                                                               0.891                                                                               0.0                               3.516 5A      18      E8    00     0.094                                                                               0.906                                                                               0.0                               3.555 5B      14      EC    00     0.078                                                                               0.922                                                                               0.0                               3.594 5C      10      F0    00     0.062                                                                               0.938                                                                               0.0                               3.633 5D      0C      F4    00     0.047                                                                               0.953                                                                               0.0                               3.672 5E      08      F8    00     0.031                                                                               0.967                                                                               0.0                               3.711 5F      04      FC    00     0.016                                                                               0.984                                                                               0.0                               3.750 60      00      FF    00     0.0  1.0  0.0                               3.789 61      00      F8    08     0.0  0.969                                                                               0.031                             3.828 62      00      F0    10     0.0  0.937                                                                               0.063                             3.867 63      00      EB    18     0.0  0.906                                                                               0.094                             3.906 64      00      E0    20     0.0  0.875                                                                               0.125                             3.945 65      00      D8    28     0.0  0.844                                                                               0.156                             3.984 66      00      D0    30     0.0  0.812                                                                               0.188                             4.023 67      00      C8    38     0.0  0.781                                                                               0.219                             4.062 68      00      C0    40     0.0  0.75 0.25                              4.102 69      00      B8    48     0.0  0.719                                                                               0.281                             4.141 6A      00      B0    50     0.0  0.687                                                                               0.313                             4.178 6B      00      A8    58     0.0  0.656                                                                               0.344                             4.219 6C      00      A0    60     0.0  0.625                                                                               0.375                             4.258 6D      00      98    68     0.0  0.594                                                                               0.406                             4.299 6E      00      90    70     0.0  0.562                                                                               0.438                             4.336 6F      00      88    78     0.0  0.531                                                                               0.469                             4.375 70      00      80    80     0.0  0.5  0.5                               4.414 71      00      78    88     0.0  0.469                                                                               0.531                             4.453 72      00      70    90     0.0  0.437                                                                               0.563                             4.492 73      00      68    98     0.0  0.406                                                                               0.594                             4.531 74      00      60    A0     0.0  0.375                                                                               0.625                             4.570 75      00      58    A8     0.0  0.344                                                                               0.656                             4.609 76      00      50    B0     0.0  0.312                                                                               0.688                             4.648 77      00      48    B8     0.0  0.281                                                                               0.719                             4.687 78      00      40    C0     0.0  0.25 0.75                              4.727 79      00      38    C8     0.0  0.219                                                                               0.781                             4.766 7A      00      30    D0     0.0  0.187                                                                               0.813                             4.805 7B      00      28    D8     0.0  0.156                                                                               0.844                             4.844 7C      00      20    E0     0.0  0.125                                                                               0.875                             4.883 7D      00      18    E8     0.0  0.094                                                                               0.906                             4.922 7E      00      10    F0     0.0  0.062                                                                               0.938                             4.961 7F      00      08    F8     0.0  0.031                                                                               0.967                             5.000 80      00      00    FF     0.0  0.0  1.0                               5.039 81      04      00    FC     0.016                                                                               0.0  0.984                             5.078 82      08      00    F8     0.031                                                                               0.0  0.969                             5.117 83      0C      00    F4     0.047                                                                               0.0  0.953                             5.156 84      10      00    F0     0.063                                                                               0.0  0.937                             5.195 85      14      00    EC     0.078                                                                               0.0  0.922                             5.234 86      18      00    E8     0.094                                                                               0.0  0.906                             5.273 87      1C      00    E4     0.109                                                                               0.0  0.891                             5.312 88      20      00    E0     0.125                                                                               0.0  0.875                             5.352 89      24      00    DC     0.141                                                                               0.0  0.859                             5.391 8A      28      00    D8     0.156                                                                               0.0  0.844                             5.430 BB      2C      00    D4     0.172                                                                               0.0  0.828                             5.469 8C      30      00    D0     0.188                                                                               0.0  0.812                             5.508 8D      34      00    CC     0.2  0.0  0.8                               5.547 8E      38      00    C8     0.219                                                                               0.0  0.781                             5.586 8F      3C      00    C4     0.234                                                                               0.0  0.766                             5.625 90      40      00    C0     0.25 0.0  0.75                              5.664 91      44      00    BC     0.266                                                                               0.0  0.734                             5.703 92      48      00    B8     0.281                                                                               0.0  0.719                             5.742 93      4C      00    B4     0.297                                                                               0.0  0.703                             5.781 94      50      00    B0     0.313                                                                               0.0  0.687                             5.820 95      54      00    AC     0.328                                                                               0.0  0.672                             5.859 96      58      00    A8     0.344                                                                               0.0  0.656                             5.898 97      5C      00    A4     0.359                                                                               0.0  0.641                             5.937 98      60      00    A0     0.375                                                                               0.0  0.625                             5.977 99      64      00    9C     0.391                                                                               0.0  0.609                             6.016 9A      68      00    98     0.406                                                                               0.0  0.594                             6.055 9B      6C      00    94     0.422                                                                               0.0  0.578                             6.094 9C      70      00    90     0.438                                                                               0.0  0.562                             6.133 9D      74      00    8C     0.453                                                                               0.0  0.547                             6.172 9E      78      00    88     0.469                                                                               0.0  0.531                             6.211 9F      7C      00    84     0.484                                                                               0.0  0.516                             6.250 A0      80      00    80     0.5  0.0  0.5                               6.289 A1      84      00    7C     0.516                                                                               0.0  0.484                             6.328 A2      88      00    78     0.531                                                                               0.0  0.469                             6.367 A3      8C      00    74     0.547                                                                               0.0  0.453                             6.406 A4      90      00    70     0.563                                                                               0.0  0.437                             6.445 A5      94      00    6C     0.578                                                                               0.0  0.422                             6.484 A6      98      00    68     0.594                                                                               0.0  0.406                             6.524 A7      9C      00    64     0.609                                                                               0.0  0.391                             6.562 A8      A0      00    60     0.625                                                                               0.0  0.375                             6.602 A9      A4      00    5C     0.641                                                                               0.0  0.359                             6.641 AA      A8      00    58     0.656                                                                               0.0  0.344                             6.680 AB      AC      00    54     0.672                                                                               0.0  0.328                             6.719 AC      B0      00    50     0.688                                                                               0.0  0.312                             6.758 AD      B4      00    4C     0.703                                                                               0.0  0.297                             6.797 AE      B8      00    48     0.719                                                                               0.0  0.281                             6.836 AF      BC      00    44     0.734                                                                               0.0  0.266                             6.875 B0      C0      00    40     0.75 0.0  0.25                              6.914 B1      C4      00    3C     0.766                                                                               0.0  0.234                             6.953 B2      C8      00    38     0.781                                                                               0.0  0.219                             6.992 B3      CC      00    34     0.797                                                                               0.0  0.203                             7.031 B4      D0      00    30     0.813                                                                               0.0  0.187                             7.070 B5      D4      00    2C     0.828                                                                               0.0  0.172                             7.109 B6      D8      00    28     0.844                                                                               0.0  0.156                             7.148 B7      DC      00    24     0.859                                                                               0.0  0.141                             7.187 B8      E0      00    20     0.875                                                                               0.0  0.125                             7.227 B9      E4      00    1C     0.891                                                                               0.0  0.109                             7.266 BA      E8      00    18     0.906                                                                               0.0  0.094                             7.305 BB      EC      00    14     0.922                                                                               0.0  0.078                             7.344 BC      F0      00    10     0.938                                                                               0.0  0.062                             7.383 BD      F4      00    0C     0.953                                                                               0.0  0.047                             7.422 BE      F8      00    08     0.967                                                                               0.0  0.031                             7.461 BF      FC      00    04     0.984                                                                               0.0  0.016                             ______________________________________                                     

What I claim is:
 1. A measuring device comprising:timing means for developing a first timing signal and a second timing signal; means for measuring a first value of a signal, in accordance with said first timing signal, and a second value of a signal, in accordance with said second timing signal, and for developing first data indicative of the measured first value of the signal and second data indicative of the measured second value of the signal; a plurality of adjacent variable color light emitting diode digital display elements for exhibiting a digital value; a memory for storing said first data, in accordance with said first timing signal; means for exhibiting on said display elements a digital indication of said second data, in accordance with said second timing signal; means for comparing, in accordance with said second timing signal, said second data with the first data stored in said memory and for developing a first comparison signal when said second data are larger than the first data stored in said memory and a second comparison signal when said second data are less than the first data stored in said memory; a color control for controlling the color of said digital indication, in accordance with said second timing signal, for illuminating said digital indication in a first color in response to said first comparison signal and in a second color in response to said second comparison signal.
 2. A measuring device comprising:timing means for developing a first timing signal and a second timing signal; means for measuring a first value of a signal, in accordance with said first timing signal, and a second value of a signal, in accordance with said second timing signal, and for developing first data indicative of the measured first value of the signal and second data indicative of the measured second value of the signal; a plurality of adjacent variable color light emitting diode digital display elements for exhibiting a digital value; a memory for storing said first data, in accordance with said first timing signal; means for exhibiting on said display elements a digital indication of said second data, in accordance with said second timing signal; means for comparing, in accordance with said second timing signal, said second data with the first data stored in said memory and for developing a first comparison signal when said second data are larger than the first data stored in said memory, a second comparison signal when said second data are less than the first data stored in said memory, and a third comparison signal when said second data are equal to the first data stored in said memory; a color control for controlling the color of said digital indication, in accordance with said second timing signal, for illuminating said digital indication in a first color in response to said first comparison signal, in a second color in response to said second comparison signal, and in a third color in response to said third comparison signal.
 3. A measuring device comprising:timing means for developing a first timing signal and a second timing signal; means for measuring a first value of a signal, in accordance with said first timing signal, and a second value of a signal, in accordance with said second timing signal, and for developing first data indicative of the measured first value of the signal and second data indicative of the measured second value of the signal; a variable color light emitting diode digital display device for exhibiting a digital value, said display device including a color control input for controlling the color of the exhibited digital value; a memory for storing said first data, in accordance with said first timing signal; means for exhibiting on said display device a digital indication of said second data, in accordance with said second timing signal; means for comparing, in accordance with said second timing signal, said second data with the first data stored in said memory and for developing a first comparison signal when said second data are larger than the first data stored in said memory and a second comparison signal when said second data are less than the first data stored in said memory; a color control for applying said first comparison signal and said second comparison signal to said color control input, in accordance with said second timing signal, for illuminating said digital indication in a first color in response to said first comparison signal and in a second color in response to said second comparison signal.
 4. A measuring device comprising:timing means for developing a first timing signal and a second timing signal; means for measuring a first value of a signal, in accordance with said first timing signal, and a second value of a signal, in accordance with said second timing signal, and for developing first data indicative of the measured first value of the signal and second data indicative of the measured second value of the signal; a variable color light emitting diode digital display device for exhibiting a digital value, said display device including a first color control input, for illuminating, upon its activation, the exhibited digital value in a first color, a second color control input, for illuminating, upon its activation, the exhibited digital value in a second color, and a third color control input, for illuminating, upon its activation, the exhibited digital value in a third color; a memory for storing said first data, in accordance with said first timing signal; means for exhibiting on said display device a digital indication of said second data, in accordance with said second timing signal; means for comparing, in accordance with said second timing signal, said second data with the first data stored in said memory and for developing a first comparison signal when said second data are larger than the first data stored in said memory, a second comparison signal when said second data are less than the first data stored in said memory, and a third comparison signal when said second data are equal to the first data stored in said memory; a color control for applying said first comparison signal, said second comparison signal, and said third comparison signal to said first color control input, said second color control input, and said third color control input, respectively, in accordance with said second timing signal, for illuminating said digital indication in a first color in response to said first comparison signal, in a second color in response to said second comparison signal, and in a third color in response to said third comparison signal.
 5. A variable color digital barometer comprising:timing means for developing a first timing signal and a second timing signal; means for measuring a first value of a barometric pressure, in accordance with said first timing signal, and a second value of a barometric pressure, in accordance with said second timing signal, and for developing first data indicative of the measured first value of the barometric pressure and second data indicative of the measured second value of the barometric pressure; a variable color light emitting diode digital display device for exhibiting a digital value; a memory for storing said first data, in accordance with said first timing signal; means for exhibiting on said display device a digital indication of said second data, in accordance with said second timing signal; means for comparing, in accordance with said second timing signal, said second data with the first data stored in said memory and for developing a first comparison signal when said second data are larger than the first data stored in said memory and a second comparison signal when said second data are less than the first data stored in said memory; a color control for controlling the color of said digital indication, in accordance with said second timing signal, for illuminating said digital indication in a first color in response to said first comparison signal and in a second color in response to said second comparison signal; whereby the measured barometric pressure is digitally indicated in a first color when the barometric pressure is rising, and in a second color when the barometric pressure is falling.
 6. A variable color digital barometer comprising:timing means for developing a first timing signal and a second timing signal; means for measuring a first value of a barometric pressure, in accordance with said first timing signal, and a second value of a barometric pressure, in accordance with said second timing signal, and for developing first data indicative of the measured first value of the barometric pressure and second data indicative of the measured second value of the barometric pressure; a variable color light emitting diode digital display device for exhibiting a digital value; a memory for storing said first data, in accordance with said first timing signal; means for exhibiting on said display device a digital indication of said second data, in accordance with said second timing signal; means for comparing, in accordance with said second timing signal, said second data with the first data stored in said memory and for developing a first comparison signal when said second data are larger than the first data stored in said memory, a second comparison signal when said second data are less than the first data stored in said memory, and a third comparison signal when said second data are equal to the first data stored in said memory; a color control for controlling the color of said digital indication, in accordance with said second timing signal, for illuminating said digital indication in a first color in response to said first comparison signal, in a second color in response to said second comparison signal, and in a third color in response to said third comparison signal; whereby the measured barometric pressure is digitally indicated in a first color when the barometric pressure is rising, in a second color when the barometric pressure is falling, and in a third color when the barometric pressure is unchanged.
 7. A variable color digital barometer comprising:timing means for developing a first timing signal and a second timing signal; means for measuring a first value of a barometric pressure, in accordance with said first timing signal, and a second value of a barometric pressure, in accordance with said second timing signal, and for developing first data indicative of the measured first value of the barometric pressure and second data indicative of the measured second value of the barometric pressure; a variable color light emitting diode digital display device for exhibiting a digital value, said display device including a color control input for controlling the color of the exhibited digital value; a memory for storing said first data, in accordance with said first timing signal; means for exhibiting on said display device a digital indication of said second data, in accordance with said second timing signal; a comparator for comparing, in accordance with said second timing signal, said second data with the first data stored in said memory and for developing a first comparison signal when said second data are larger than the first data stored in said memory and a second comparison signal when said second data are less than the first data stored in said memory; a color control for applying said first comparison signal and said second comparison signal to said color control input, in accordance with said second timing signal, for illuminating said digital indication in a first color in response to said first comparison signal and in a second color in response to said second comparison signal; whereby the measured barometric pressure is digitally indicated in a first color when the barometric pressure is rising, and in a second color when the barometric pressure is falling.
 8. A variable color digital barometer comprising:timing means for developing a first timing signal and a second timing signal; means for measuring a first value of a barometric pressure, in accordance with said first timing signal, and a second value of a barometric pressure, in accordance with said second timing signal, and for developing first data indicative of the measured first value of the barometric pressure and second data indicative of the measured second value of the barometric pressure; a variable color light emitting diode digital display device for exhibiting a digital value, said display device including a first color control input, for illuminating, upon its activation, the exhibited digital value in a first color, a second color control input, for illuminating, upon its activation, the exhibited digital value in a second color, and a third color control input, for illuminating, upon its activation, the exhibited digital value in a third color; a memory for storing said first data, in accordance with said first timing signal; means for exhibiting on said display device a digital indication of said second data, in accordance with said second timing signal; a comparator for comparing, in accordance with said second timing signal, said second data with the first data stored in said memory and for developing a first comparison signal when said second data are larger than the first data stored in said memory, a second comparison signal when said second data are less than the first data stored in said memory, and a third comparison signal when said second data are equal to the first data stored in said memory; a color control for applying said first comparison signal, said second comparison signal, and said third comparison signal to said first color control input, said second color control input, and said third color control input, respectively, in accordance with said second timing signal, for illuminating said digital indication in a first color in response to said first comparison signal, in a second color in response to said second comparison signal, and in a third color in response to said third comparison signal; whereby the measured barometric pressure is digitally indicated in a first color when the barometric pressure is rising, in a second color when the barometric pressure is falling, and in a third color when the barometric pressure is unchanged. 